If McCain or Obama Died....?

I was thinking... in this world we live in, no one is 100% safe. People die all the time from health problems, violence, or accident.

What would if Obama were to die now before choosing His VP candidate?
What if Obama dies after a VP candidate is chosen? Does that person become The Presidential candidate and therefore must choose a new VP running mate?
What id McCain were to die before choosing His VP Candidate?
What if McCain dies after a VP candidate is chosen?

Would special primary elections be held? Who would be the judge? Is there a precedent?

I worry that some little-thought-of political maneuvering could turn our little world upside down. In a way no one would have ever seen coming.

I have no knowledge of the policy or procedure for rules pertaining to such an event.

What do you think would be the procedure in such cases? Who would be next in line?

I figure the party would just find a new nominee. I'm sure there's rules about it, but I'm a lazy camel.

There must be some people here on ATS who have got a good idea about this.... Lets have some input! Please

Neither McCain or Obama are yet their respective parties official nominee. They are the presumptive nominee, meaning that barring anything unfortunate happening between now and the party conventions, they will most likely be named the official nominee.

If something were to happen before the conventions that would prevent them from serving as the nominee, it would fall on the parties at their convention to select a new nominee. Even if there was already a VP candidate selected, it would still fall on the party to name a new nominee at the convention.

To be honest if they were both to die the United States would be a better place. Now the chances of that happening are not that good so I would even get worked up about it.