I honestly don't believe there's anyway he goes to Chelsea at any point in the future. Even as our leading PL scorer he just wouldn't be welcome back as a a "Legend" at any point if he did that, which is something a lot of players even more recent ones like Defoe seem to really enjoy.The "would you rather he go to our rivals for nothing" doesn't really faze me: as we've seen with Poch, once someone's gone we can't dictate where he goes. There's absolutely nothing saying he goes to Bayern this summer, doesn't settle and Chelsea offer him an escape. He's here or he's not, basically.
It would be pure S** C****** level and if things didn't work out at Chelsea he'd have ruined his legacy for nothing. If he went to United or Newcastle (or any team abroad) for nothing in a year, it would be bad but not legacy destroying.