Unit only empires

[Saxon]

Cynical question coming up. If you have gotten so knocked out of the game that you are down to ships only, what are your realistic chances of coming back to do anything significant? Given the exponential growth that most empires depend on, could you catch up again?

I am thinking that in a close fight, an ally who colonized different planets might help you out. Or in a game with unusual victory conditions you might be able to help. However, in a traditional, big dog on top wins, game, would it be realistic to expect to get anywhere? An ally would only let you get so big before eating you up and whoever glassed your planets is will be way ahead of you.

Not having played much against other humans, I would be interested to hear about situations where you might be able to do something in this situation.