Unless they plan to promote him to HC when the new HC, whomever that is who takes the job, they will want to hire their own guys, at QB Coach as well
If he's the key to keeping Watson, then maybe he's a condition of the job for the new guy. He might also be the fallback HC option if they can't find an alternative. I don't know the guy at all but he looks like he's been on a fairly good career trajectory there, going from an offensive assistant in 2015 via assistant OL and then TE coach, to OC for the last two years and also QB coach last year, so he's presumably tight with Watson. He's still only 34 as well.