Not a Rhodes scholar and have not played one on TV.
Shep was not a bust. Perhaps misused or did not skill for scheme he was required to play but not a bust. He was not cut when new coaching staff came in and they cut unceremoniously players which new coaching staff had no use for even if other teams did and signed them. It appears that he was going to compete in training camp. Either they kept him thinking he was useful, even if just for depth or special teams, or they saw his combination of skills/contract would be appealing to another team to trade picks/player for.
I'd be interested in when the talks started.