I think the Steelers will just wait until about mid-season or a few weeks after that to determine who their quarterback 'of the future' is going to be. If Wilson can still play at a high level, they'll ink him to a 3-4 year deal, and they'll let Fields become a free agent. If they feel that Fields is playing better or has the potential to do so more than what Wilson shows on the field, they'll commit to Fields long-term.
Strategically, it's a pretty good place for Pittsburgh to be in.