If Cavill is going to be Superman, I guess this means he won't follow up Daniel Craig as Bond. Now that can really be Fassbender.
I don't see why not. Cavill's only 27 right now; he probably needs a few more years on him before he'll really be right for the role, but the rumor is he was very close to getting the role in Casino Royale
before the producers (wisely) decided to go with the older Daniel Craig. If Bond 23
(for lack of an actual title) proves to be successful in 2012, I'm sure Craig will be back for at least one more outing. Given Craig's age by that time (he turns 43 in a few weeks), I can see him calling it quits after that.
So presumably we'll be looking at a new James Bond sometime around 2017 or 2018. Henry Cavill will be in his mid-thirties by then, and I don't see why he couldn't play both James Bond and Superman. Especially since (if this new take on the character becomes a trilogy, for example) by then, he might be done, or close to being done, playing the latter character.