In a perfect world, I think you re-sign Wilson but draft a QB in round 1 to sit behind him for a year or 2. The mock draft website I use (Walter Football) has the Steelers taking Milroe at 25, I think drafting Milroe and sitting him behind Wilson for 2 years is an excellent option. The thing that concerns me though is that I think Milroe at 25 is a bit of a reach, but I don't think he'd be lasting until their 2nd rounder.
If they could do it, I'd probably trade down with their 1st for an early 2nd and another pick to draft Milroe with that early 2nd. Have Milroe learn from Wilson for like 2 years and then hand the starting QB role over to him.