I don't think Burton was ever safe, the real talk started mid year. Fagan really pushed for the review, he was obviously listening to the groundswell.
Campo is harder to judge, some players really rate him. I think as the group was set for a huge change it was clear he wasn't equipped for it. Had a lot of credits after 2015 but burnt them all and then some.
Fagan may get a pass as he called for the review (despite Chapman claiming this as his decision)
I believe Campo was liked by senior players but not so much with younger players. This is based on observations and rumours not inside info this.