They weren't really dead, just close to it.

So you're talking about reviving people who have been totally dead for long periods of time. That would probably require scifi technology so there's not much point discussing it.

Some evidence that there could be is not enough.

I didn't intend for that to be definitive proof, just letting you know that there is some physical evidence out there and the multiverse theory isn't just some physicists sitting around playing with math.

Why are we even postulating things we cannot observe even in principle?

This really sounds more like a question that would be better directed at theists...

Is it just trying to explain away the fine tuning argument?

The fine-tuning argument doesn't need to be explained away because it's bunk. OF COURSE the laws of physics in our universe seem fine-tuned for life as we know it. We arise in this universe and so to survive we have to fit those laws.

If some of the universal constants were different, for example if gravity were twice as strong, then the sun would have used up it's fuel and burned out already, probably destroying the earth in the process. But jupiter would itself be a tiny sun with a mini-solar system orbiting it. If life arose there then they would wonder at how fine-tuned the universe is for them because if gravity weren't as strong their sun would never have started burning.

For further explanation of why you shouldn't use the fine tuning argument, I direct you to Douglas Adams:

Imagine a puddle waking up one morning and thinking, "This is an interesting world I find myself in — an interesting hole I find myself in — fits me rather neatly, doesn't it? In fact it fits me staggeringly well, must have been made to have me in it!" This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, it's still frantically hanging on to the notion that everything's going to be alright, because this world was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise.