I still doubt Pettine gets fired in-season, but I would guess that he doesn't come back next year. With that in mind, I want to start spot-lighting some DC candidates.
One interesting guy is the 49ers' DL Coach, Kris Kocurek.
Kocurek was a DT at Texas Tech, drafted by the Seahawks in 2001 in the 7th round. He kicked around the league a couple of seasons before returning to TTU as a graduate assistant coach in 2003.
He was a small school DL coach for Texas AM Commerce (2006), West Texas AM (2007), and Stephen F. Austin (2008), before joining the Lions as an Assistant DL coach in 2009.
He took over the lead DL Coach job in Detroit in 2010, and remained in that role through 2017. During that time span, the Lions' DL accounted for 250 sacks (31/season), which was the 4th most of any DL in the league over that span.
He then spent the 2018 season as the DL coach for the Dolphins.
In 2019, he joined the 49ers in the same capacity.
Seems to me there is a trend with him of getting the most out of his players. For instance, Ziggy Ansah had 44 sacks for Kocurek in five seasons, and then 6.5 in three seasons since. Arik Armstead had 9 sacks in his first four seasons, and then 10 in his first season under Kocurek. He got 6.5 sacks out of Anthony Zettel in 2017, who has done literally nothing otherwise. He also coached Kerry Hyder to an 8 sack season.
I have no idea if he has the aptitude to be a DC, as being a good teacher at a given position doesn't mean you have the skills to coordinate an entire unit. But he's done a really good job in his role everywhere he's been, and he's worked under some pretty accomplished DC's (Jim Schwartz, Teryl Austin, Robert Saleh).