Oh, but Gryphin, what is more fun than winning?
Yes, Tbon, your analysis is probably correct for the most part. Of course there are always the loners who will want to go it alone, and will gain pride form being able to, or at least attempting to. But likely they will not survive.
Something else to remember is it is possible you could "hide", stay isolated to a couple systems in an out of the way corner and hope no one notices you. If someone finds you, bluffing is often useful. "Why yes, I have an alliance, he's right over there. No I'm afraid I can't let you go that way, that system is restricted by order of the emporer."
It might not work, but it would be fun to try. And it only has to work long enough for one of the alliances to pick off some other loner, or a weak member of another alliance. Or for that matter to get an alliance to turn on one of it's own. That's always fun.
Geoschmo