I don’t see the players on hand as “the swamp.” Addazio didn’t put them in a position to succeed.
In the case of the players who are good enough to transfer to other P5 programs, I’d argue that the program needs them more than they need the program. A few departures are inevitable, and probably best for all concerned, but the Hafley era will be doomed from the outset if he doesn’t keep most of the 20 or so best returning players. Even the best coaching won’t coax more than 3 or 4 wins out of a team of 18 and 19 year olds, and even Nick Saban couldn’t convince elite recruits to join a 3-win team in Chestnut Hill. Hafley needs the incumbents (or most of them) to buy in.
Fortunately, I don’t think a mass exodus is terribly likely. Even if the players liked Daz, and I assume most did, the silent majority of them had to chafe at how he didn’t trust them to make plays on offense and cost them games with boneheaded decisions. A few guys will make the NFL, and I’m sure a few others mistakenly think they will, but for most of them, this will be their last football team, and they know it. They want to win more than anyone. And they can see as plainly as anyone that Daz didn’t put them in the best position to do that. Hafley is more likely to enjoy a honeymoon than to face a mass exodus.