Alex Rodriguez would be a fool not to opt out of his contract 10 days after the end of the World Series. This year, at 32, he enjoyed his greatest season yet at the plate. He will never again have the leverage he would this fall — and he will never again need as much as he has now. A new contract would probably determine where he’ll spend the rest of his career.

Because of baseball’s popularity, revenue sharing, and the cash raised by the game’s online presence, there is more money in baseball than teams can spend. In 2000, when Rodriguez signed a contract making him baseball’s first $25 million a year man, the highest paid player in baseball was Kevin Brown, who made $15 million. These days, merely solid players like Houston’s Carlos Lee are making $19 million per year. Rodriguez is in for a big raise, and the best way to find out how big it can get is to let teams compete for him.

General manager Brian Cashman said last week, “If Alex Rodriguez opts out of his contract, we will not participate in his free agency. That is accurate and that is definitive.”

So, one of two things will happen: Either Rodriguez will opt out and join another team, or the Yankees will offer him so much money he’ll pass up the chance to even hear what the Boston Red Sox or the Los Angeles teams have to say. A deal so good it couldn’t possibly be topped — one would have to think that would be north of $300 million.

Can anyone imagine the same Yankees brass — one that couldn’t even figure out whether or not to offer legendary manager Joe Torre a contract — working out a $300 million deal in the next two weeks? The most important question for the Yankees right now is neither who should manage the team nor how much to offer Rodriguez: It’s how to replace the best player in the sport.

The most basic fact about the team’s lineup is that even with Rodriguez returning, it would need much luck to be as good again next year as it was this year. Not only did he produce as he never had before, Jorge Posada had also, by far, the best offensive season of any catcher 35 or older in history, hitting .338 with walks and power and playing an amazing 144 games. If Posada and Rodriguez were to return and post seasons halfway between what they did in 2006 and what they did in 2007, the Yankees would decline by about 45 runs.

Where would they make those runs up? Derek Jeter, Hideki Matsui, Jason Giambi, Bobby Abreu, and Johnny Damon are all aging. It’s easy to imagine one or two of them playing with more verve next year. But collectively, they’ll likely play about as well next year as they did this year, or a bit worse. Robinson Cano and Melky Cabrera are good and young, but neither is about to break out as a franchise hitter. Unless the Yankees both resign Rodriguez and bring in some monster to play first base — and there is evidence over many years to suggest they think no such thing is necessary — it’s difficult to see how they’ll match this year’s performance next year. Returning the same lineup with even a decent hitter such as Wilson Betemit at third could easily cost them five to ten wins just on offense.

A run saved is at least as good as a run scored, of course, opening up all sorts of possibilities. But to confidently make up for an expected five to 10 wins worth of lost offense, the Yankees need to make an average staff as good as Boston’s. Basically, they’d have to build a lights-out bullpen and see two succeed as rookie starters from among Joba Chamberlain, Philip Hughes, and Ian Kennedy. And they’d have to trade for Minnesota’s Johan Santana.

There is a middle way here, which would involve acquiring a hitter of, say, Adam Dunn’s level to play first base, some good relievers, and a decent no. 3 starter capable of pitching 200 innings. Assuming Cano and Cabrera improve; Jeter, Damon, and Giambi all pick up their games a bit, and the three young pitchers prove to have 300 solid innings in them, the Yankees would do about as well next year as this year — even without Rodriguez.

The whole catch, though, is in that team representing the American League in tonight’s game. The Yankees are playing from behind as is. Being as good as they were this year might not even get the Yankees in the playoffs next year. If they’re playing for first place, they’ll need to keep Rodriguez and improve elsewhere just to keep pace with a Red Sox team that’s young enough to get better with time. If the Yankees aren’t, then there will be an awful lot of questions to be answered about what exactly they are doing.

tmarchman@nysun.com