Bill actually had a trade in place with Patricia/Lions for a 1st round pick. When Gronk found out, he told the Pats he was retiring so the Lions backed out. If the trade went down, I think they definitely would've taken Lamar Jackson with one of their 3 first round picks.
I'm not a fan of trading key players on a good team when there was much at stake. Pats had a weakening defense and trading Seymour was not a good move, even for a 1st round pick which is unknown. Not only that, they couldn't use it for two years after the trade went down. I'd take two good years of Seymour and potentially making a difference in the playoffs vs the Jets/Giants than for a player who is an unknown.
Chandler Jones was an even worse trade. He was an ascending Pro Bowl (future All Pro and runner up for DPOY) player at 25 years old, but they traded him for a measly 2nd round pick and bust OL as a throw in? I would've at least kept him for 2016 and let him go after that season if his contract demands where too high.
Shaq Mason was alright, but his trade created a need at G which they then blew a 1st round pick on.