I believe they will. Unless there was fraudulent intent, IRS has 3 years to audit a return. I imagine that there was a change of address for that year. That clearly (to me) indicates that the home that had the credit was no longer being used as a primary residence and that the credit was due to be paid back. I think that the sale of a home was probably reported - Again everything IRS needed to do their job right.  IRS had sufficient evidence to take care of this properly. They dropped the ball. You are just helping them clear up any concerns that they might have.
Alternatively, do nothing. Don't bother with all the paperwork. Maybe file for the open years to get the annual payment back. Those early years are closed. Do 2015 & 2016 & 2017 (gotta hurry on 2015)