My bad.
Still the Brewers are not generally in the business of giving MLB contracts to guys to sit in AAA or on the bench. If he's extended, I would expect him to be called up soon and be seeing significant MLB ABs, almost certainly at the expense of Frelick.
With Chourio, Mitchell, and Bauers already taking up the lion's share of ABs, it becomes a simple numbers game. Would they need to trade Frelick? No, especially with Mitchell's health always in question. But he would become a 4th/5th OFer and likely be on his way out sooner than later.