Do you agree that it spells out that the FT has exactly two win conditions?
- Complete mission and escape via the chopper.
- Down the Predator and secure the body.
I agree that is does not explicitly say that a self destruct is a Predator win (though the end screen seems to indicate that it is) it is certainly not a FT win condition and there is no mention of a draw/tie anywhere.
For the Predator I interpret those rules as also having exactly two win conditions.
- Eliminate the entire FT as even one escaping is a Predator loss.
- Successfully self destruct.
If the FT are all alive at the end of the match and have none have escaped in the chopper, Predator gets the Fire Team Eliminated end screen. The same screen as if he has killed them all. That would indicate to me to be a win condition.
So the answer the story question about “what happens after the match ends and there are still FT on the ground” is that the Predator kills them after the chopper has left.
So in a nut shell, if even one out of four FT gets a win condition, it is a loss for the Predator.