Can Mitt Romney re-enter the Republican presidential nomination race?

1. The new accusations regarding John McCain and a female lobbyist cause his Presidential campaign to nosedive, or

2. McCain ends his Presidential campaign for whatever reason (health issues, scandal, etc.)

Can Mitt Romney jump back into the race? From what I recall, he technically “suspended” his campaign.

What would happen to McCain’s delegates if McCain ended his campaign?

If McCain did not end his campaign, could his delegates bail on him?

Obama