You all are making a huge assumption. There is no guarantee that Luck will even come out this year. Would you with all the uncertainty of 2011 NFL? Hes only a Soph (albeit a RS Soph). Sure if he comes out I don't see how we could pass on him but it is by no means a sure thing.
I think Harbaugh wouldn't leave unless he knew Luck was going to declare. Not saying he doesn't think he can win without him but why leave when you have unfinished business (no NC) and the best College QB in recent memory (at least in my eyes). But if he does declare and we have the 1st pick we have a powerful incentive in trying to convince him to coach here in the NFL.
This team to me is made for Harbuagh great RB's, a great (when healthy + a decent RG) and some good young WRs. Even a pretty good D if he keeps Meeks and stays in the 4-3. Add a franchise QB like luck and all of the sudden this team looks dangerous (maybe not year 1). Maybe just maybe the stars are aligning in our favor.