I don't think I'd ever give my players the option of fixing the apocalypse.
I'll mostly agree. I doubt that most (if any) of our gaming groups have anyone with the necessary skills and knowledge to fix a zombie apocalypse (depending on the cause). But it might make for some interesting scenarios if in addition to surviving, the players have an idea what is causing the "plague" and devote time to trying to gather the resources (including finding and rescuing experts) who might be able to come up with a solution.
step 1: play as a average Joe, plumber.
step 2: somehow fix the apocalypse.
step 3: Bill the remaining governements of the world with the words: "Yeah I've fixed yer zombie problem, but it wasn't cheap."