Not many football clubs get to dictate the ends of eras. And Arsenal, exceptional for so many years, is no exception.

Years of mismanagement have left it with just two standout stars, each with less than six months to run on his contract; with a 68-year-old manager who’ll likely be gone in a few years; and with no clear path forward. No plan. No direction. Very few mechanisms to cope with ongoing decline.

But there is one thing Arsenal can control. It can dictate the timeline. It can decide when the end begins.

It can decide whether one last uphill battle is worth charging into. Rather, it has to decide. And soon.

It must decide whether those two stars, Mesut Ozil and Alexis Sanchez, are worth hanging on to for five more months. In a way, it’s two separate decisions; while Sanchez looks sure to leave, Ozil could yet stay. But in another sense, it’s one large decision about direction, aspirations and identity. And the deadline for making it strikes in three weeks.

Arsenal must decide whether to sell Sanchez in January. Because Ozil’s situation is less clear, we’ll limit analysis to the Chilean. He has reportedly agreed terms with Manchester City. If Arsenal does sell, it will sell to City; if it doesn’t, Sanchez will almost surely join the soon-to-be Premier League champions on a free in July.

It’s a no-win situation for the Gunners. Either they lose one of their best players for the stretch run, or lose him without compensation. The club has backed itself into a corner.

To figure out how it should escape, it’s first worth looking back at how it arrived at the corner. Because the decision staring it in the face right now is very similar to the one it botched six months ago.

Why has it come to this?

Arsenal went into the summer knowing that Sanchez’s and Ozil’s contracts would expire at the end of the 2017-18 season. It also presumably knew that riding contracts into their final years generally isn’t best practice. And hopefully it knew that Sanchez intended to leave – because that was clear even from the outside.

Arsenal should have sold Sanchez. It should have sold Ozil, too. It’s not easy for a club to part with its two best players, but 99 percent of European teams, at one point or another, do. Arsenal isn’t above that. Players outgrow clubs. There’s a hierarchy. And Arsenal isn’t on top of it.

Everywhere below the top, clubs sustain themselves by selling top players for profits and reinvesting the cash in others. They might push back, but they give in while the player’s value is near its peak. Liverpool, for example, sold Luis Suarez with four years left on his contract, Raheem Sterling with two years left, and Philippe Coutinho with four years remaining.

Arsenal, on the other hand, hasn’t sold a regular starter with more than 12 months left on his contract since Alex Song ­– to Barcelona for $20.3 million – in 2012. That same summer, the Gunners also let Robin van Persie, at the height of his powers, join Manchester United for just $32.4 million. The reason for the bargain-bin price? Van Persie had just one year left on his deal, and told Arsenal he wouldn’t be signing a new one.

Five years later, the Gunners could have turned over at least $74 million for Sanchez in a similar situation. But it took them until late in the window to overcome their stubbornness. With less than 48 hours to go, they reportedly agreed a fee with City, but the deal hinged on Arsenal finding a replacement. It ultimately went way out of its price range for Thomas Lemar, only to have Lemar reject the move.

So here we are. Five months later, Sanchez’s price has been slashed in half, because five more months down the road it will be nonexistent. Arsenal is in sixth place, five points off fourth. And Sanchez, who’s been his usual sparkling self, is vital to the top-four challenge.

But is half a season of Sanchez worth $35 million, the rumored price tag?

Alas, it’s a bit more complicated than that.

What factors should Arsenal consider?

There are so many ways to assess the decision. The best is to break down the economics of it.

If we go from a baseline of Arsenal missing out on Europe, selling Sanchez is worth around $35 million. Simple. That’s the amount, give or take a few million, that Arsenal will recoup.

The other option, holding onto him, can be appraised in terms of Arsenal’s 2018-19 Champions League hopes.

The bottom-line difference between the Champions League and Europa League is significant. In 2017-18, the average Champions League participant will get a revenue share of $49.2 million. The average Europa League participant will get a revenue share of around $9.9 million. For Arsenal – a knockout-round mainstay from the largest TV market – those projections are more realistically around $60 million and $15 million.

That’s a $45 million estimated difference – larger than any potential Sanchez fee. But Sanchez isn’t the difference between the Champions League and the Europa League. Let’s say, between its top-four odds (~30 percent) and 2017 Europa League title odds (~10 percent), Arsenal has a 40 percent chance of qualifying for next season’s Champions League with Sanchez. Let’s say those odds dip to around 20 percent without Sanchez. Keeping Sanchez, in that sense is worth just $9 million – 20 percent of 45.

But then there are the knock-on effects. How many more tickets can Arsenal sell, and at how much higher a price, in the Champions League vs. the Europa League? How much more are sponsors willing to pay? How much is the prestige of the Champions League worth in merchandise sales?

Not even Arsenal has the answers to those questions yet, because it has never completed a full year in the modern-era Europa League. But those are some of the questions executives will ask themselves.

Those numbers likely still don’t add up to $45 million. But they also don’t fully represent the value of the Champions League. Which brings us to how Arsenal should approach this.

So what should Arsenal do?

The August deadline-day hang-up still applies. Arsenal, when it loses Sanchez, will need a replacement – either immediately, or in the summer.

The unquantifiable aspect of the Champions League vs. Europa League distinction is the role the top continental competition plays in a club’s ability to attract players. For example: If both Arsenal and Liverpool offer similar packages for Lemar in July, but the Gunners have finished sixth and Liverpool fourth, how are they going to get their hypothetical top target? In other words, is a Champions League spot a prerequisite for adequately replacing Sanchez?

On a more macro level: Is staying afloat, on the fringes of the top four, necessary? If the ultimate goal is competing for Premier League titles, is bottoming out – in sixth, well off the top-four pace – a major setback? Is it significantly harder to build from there than from where the club is right now?

Probably not. But the logical solution here is to sell Sanchez, and buy his replacement in January, with the top four and a Europa League run still within reach. Pitch a young winger with promise – in the 22-26 age range, such as Lyon’s Nabil Fekir – on the possibility of Champions League football, but also on the long-term project.

And, crucially, buy and sell in the right order. In the summer, Arsenal navigated the situation backwards. This time around, Arsene Wenger’s first move should be to identify and strike a deal for the replacement. Then go to City, without the worry that the Sanchez cash will drive up the replacement’s price, and negotiate the sale.

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Henry Bushnell covers global soccer, and occasionally other ball games, for Yahoo Sports. Have a tip? Question? Comment? Email him at henrydbushnell@gmail.com or follow him on Twitter @HenryBushnell.