I've heard comments on his contract so I did a search for more information. There is a clause that states his team cannot extend him a qualifying offer, which means the Mets won't get a draft pick from whoever he signs with next season. That doesn't mean the Mets cannot resign him, just that more teams will be tempted to bid for his services. There are a few other big names coming on the outfield free agent market, mainly Justin Upton, Alex Gordon, and Jason Heyward. If things work out well with Cespedes and the Mets this season, we can make a run at resigning him.
If he winds up signing with the Yankees, it'll be interesting to see the reaction of those who have been criticizing him as a bad clubhouse guy.