As a fellow Diggs owner I totally get your conundrum. I've gone back and forth about Diggs not playing the same amount of snaps the last few weeks, and the BIlls' change in Offensive Coordinator causing a reduction in passing and a renewed focus on their run game (which can be argued has caused a lack of mojo for Josh Allen when he has to throw), and the overall reduction in the passing game. Diggs is still seeing a high percentage of the passing pie, but the pie itself has been reduced a little.
However.... the last 4 games against the Patriots Diggs has had double-digit fantasy points and has had good games w/TDs. At the end of last year he was having a good year and then the final 5 games or so his fantasy numbers were around 3 points - 5 points... sound familiar? Then week 18 he played the Patriots and blew up against them with 10 targets, 7 catches and a TD.
Plus, the Patriots won't allow Cook to run efficiently against them so I see them needing to lean on the passing game more than they have the past few weeks, and I would also leave Diggs in your lineup, as I also am doing.