They'll find guys. Good teams lose coordinators all the time. If the head coach is legit, which I think Campbell is, they'll find replacements.
Not saying it's happening in this thread but you can tell a lot of people only follow Lions news and have no idea what happens in the rest of the league. Nearly every contending team right now has lost coordinators and replaced them, often in house, without missing a beat. Bills, Ravens, Niners, Cincy, Tampa Bay, etc have all found guys without issue.
Only question I have is whether Dennis Allen is gonna replace Glenn or if we go with someone in house (the linebackers coach seems like the guy getting the most buzz).