If Craig Smith goes down, it's unlikely they hire a replacement from within. So then Burgess is stuck looking to find an opening on the BYU staff next year (when it's less likely to be open) or convince the new Utah coach to retain him.
If he leaves now, goes to BYU and BYU has a good year, then he's not only increased his job security, he's given himself a better potential path to the Utah HC job