User blog comment:Commdor/Questions for Mass Effect 3/@comment-2250460-20110411054133/@comment-1853169-20110411062533

All we know so far for the likes of Mordin and Legion (and others) is that they were be back in some capacity if, as JakePT pointed out, they survived the Suicide Mission. They might be full-fledged squad-members or only temporary for a mission or so. We obviously don't know the specifics yet but that is what Bioware has said thus far on the topic in the Gameinformer issue.