But how do you play a dead person?
Aside from that mirror reflection scene that is?
They'll probably find another Green Goblin actor anyway
if they decide to bring him back.
Especially since they've "closed the book" on that version of Spider Man and started a retcon.
I did read somewhere that the Green Goblin is hard to kill, because of the mutations he experienced when exposed to the gas.
So even if he gets fatally injured, he will recover, but it will take a while, because he doesn't heal as fast as Wolverine.