Well, there's Liara. Depending on the number of survivors, she could habor the children of potentially a dozen or more. Then (for the greater good, I guess) every human crew member with each other. But even in this scenario Team Dextro dies a slow death at best, Tali won't even have a child I imagine (albeit given the... perticular... way Asari reproduce, maybe she wouldn't need to get out of her suit?). I know nothing about such things, so I doubt it can produce a viable population, but hey one can hope at this point.
One thing that is extremely sad? EDI. If everybody dies, she is left all alone for... well until her batteries run out or somesuch. In that case I certainly hope she can shut herself down.
Really, the more you think about it, the more depressing this get. I like the endings, I like the sacrifices demanded, but what happens to our crew is just going overboard, Bioware. They should at least be stranded on Earth, and whenever you have a high Readiness rating determines how many people are left alive to help them (from a reasonably high number to absolutely nobody). Hell, the crew could rally the survivors of their vicinity and build a city, eventually a nation. Maybe find some food or even, err, company suitable for Team Dextro. The ending would still be bleak, but with a beacon of hope.