There was a time jump of many years after the scene of Rick and the bridge blowing up. They show has not exactly explained what happened yet but the fall of Sanctuary seems to have occurred in those years.

 

Didn't Carol torch a good number of the remaining Saviors? Negan found the zombified remains of a few others who may have met their demise in any number of ways. I'm not sure it's really important except to show Negan that his empire was dust.

 

Lol @HungryZombie answered by saying we aren't exactly sure what happened yet.

 

Well we knew that before Sanctuary's demise that the other groups were keeping it afloat by providing them with food. We know Sanctuary had a fight at the bridge where likely a lot of lives were lost. So we can conclude that since the Sanctuary folks lost the camp fight, and could not sustain itself that they likely disbanded into smaller groups, one of which gets killed off by Carol