In historical times, sometimes you see conquest followed by elite dominance: the winners are outnumbered by those they’ve conquered, but rule them for some time. Usually they eventually dissolve into the majority population. Sometimes the top dogs lose their language (Bulgaria, Mitanni, Rus), sometimes they manage to impose it on their subjects (Ottoman Empire, Hungary) .
Other times, the invaders come close to completely replacing the previous owners. In a case like that, I would be seriously surprised if they adopted the language of those they rolled over. Sure, they’d pick up a few place names, maybe some specialized words: but they wouldn’t adopt the losers’ language.