At this point just taking any and all opponents planets as fast as possible is what I would do, though the situation as you describe it is pretty bleak. Assumedly you've tried to get peace with as many as possible and that's failed. If not then do so quickly.

This also points out the value of having convenient save games so you could possibly back up to before everyone was pissed off at you and this time not do whatever it was that pissed them off to begin with.

It's worthwhile to try to fight your way out of it first though. It's amazing how well you can do sometimes, concentrate on the weakest, run away from the strongest. Remember you don't have to keep them from taking your planets, you only have to take theirs faster than they take yours. Good Luck, but these dire situations can also turn out to be some of the best games you'll have.

CTRL-N

  

I'd calm down by playing Space Rangers 2 for a while, then start a new GC2 game at a lower difficulty level. It's better for the ole blood pressure, you know. heh.

If I lose. I'll die fighting.

That's the spirit. Even if (or when) you lose, situations like this are good learning experiences, you might even surprise yourself and win.