Ending Game
People who watch their robots in action against other comparable robots notice little places where they could have done to win a round they lost. The first kind of ending game would therefore be making a comeback. Of course, the second kind of ending game is preventing a comeback when you're ahead.
Making a Comeback
I've seen a lot of robots that stop firing when they have low energy (they may allow themselves to become disabled, and then they're pretty much sure to lose) and just dodge around. Since most top bots don't hit each other very much, it works enough of the time to be good. Of course, it seems like the dodging bot still ends up losing most of these rounds, so maybe they should just keep shooting and get a few more bullet damage points. They can move further away, though (don't have to worry about missing if you're not firing), and sometimes it works. Maybe even often enough to make it worth it. It's certainly satisfying to watch that occasional comeback.
Preventing a Comeback
I have to admit, that satisfaction doesn't come when I'm watching Cigaret come back against one of my bots. It's particularly humiliating if I was ahead 40 to 2 before I wasted all my energy unable to hit that thing. Keep in mind that an opponent with 1/8 of your energy (or even 1/5) is really unlikely to ever come back unless you let him. If they keep shooting full-power bullets, they'll be disable before long, and if they start shooting low-power bullets, they can hit you all they want as long as YOU HIT THEM, TOO, with a higher-powered bullet. It's probably a good strategy to advance on an enemy who is near dead, just to make sure they don't pull a fast one on you.
As long as you shoot just hard enough to finish off your opponent you don't really need to worry about a comeback. You shoot fast bullets en masse and need only hit with one to end the game. Sometimes it might be prolonged by a stray hit from your opponent, but seldom to the point where you actually lose the round.