Hypothetical question for those who are more educated in Political Science than myself.

First of all, in no way am I condoning this as a revolutionary idea or anything of the sort, I am just curious and asking about a hypothetical situation.

If a member of the electoral college dies, who replaces them? And how soon is this person promoted to the position?

Why I am wondering? What if a massive hit on all or most of the electors was carried out simultaneously in an attempt to sway an election one way or another despite popular vote. Would it be possible to know who the replacements would be and know ahead of time or buy their vote to basically make someone president who may not come anywhere near to winning the popular vote?

I would assume the election would be delayed and what not, but just out of curiosity, how do you all think this hypothetical situation would play out, and would it be possible for a no name candidate, or massive underdog, to win based on owning the replacement votes?