5. Robert Saleh
As a Dearborn, Michigan native, and with the success he had as the San Francisco 49ers defensive coordinator, Saleh was an appealing candidate to take over as the Lions' head coach. A clear players' coach, he could have been seen in the same vein as Campbell in that way alone.
Saleh wound up going to the New York Jets. Expectations were high going into this season, after the acquisition of Aaron Rodgers. Rodgers didn't last five snaps into Week 1, and things went downhill on the way to a 7-10 record. Over three seasons in New York, Saleh is 18-33 with zero playoff appearances. If not for the Jets being so beholden to Rodgers for at least another year, he would probably have been fired after this season.
It's possible Saleh would have pretty good results three years into as hypothetical tenure as the head coach in Detroit, as long as he had hired the right offensive coordinator (and didn't lose him to a head coaching job).
But Campbell had history with Ben Johnson from their time together on the Miami Dolphins' staff, and kept him from Patricia's previous staff as the tight ends coach. Maybe Johnson would not have been compelled to stay on under Saleh, whereas he was when Campbell was hired. Sometimes things just work out they way they are supposed to. Saleh not coming back to Michigan to be the Lions' head coach was not meant to be.