Honestly the entire thing is moot at this point but, from all of the comments I've read, nobody seems to have mentioned that his contribution to Prop 8 could be based on his personal religious beliefs.
If anything (and there is no signs of him doing so at this point), he could press on the Federal level a case of discrimination for violating his Civil Rights based on the religious aspect alone.
He would probably also win if there was even a slight whiff of him having been pressured into resigning because of this. Race, religion, gender = the big three when it comes to discrimination lawsuits and highest on the no-no scale of what companies can fire for/pressure over.