What about player(s) like McCoy/Nsekhe/Zay and a conditional 2nd that turns into a 1st if he is re-signed? I feel like the players aren't missed since they're older and/or redundant and losing the pick hurts just enough to make sense for me.
If Cowney walks in free agency you basically swap a 2nd for a 3rd for one year of Clowney (without going into franchise tag options).
If he stays, a huge need would be filled. The 1st round pick would probably be used on a pass rusher anyway. You never know how that player will turn out and how long it will take them to reach their prime. Clowney is more of a sure thing.
As for the salary difference, it doesn't matter much since Buffalo has plenty of space for the next couple of years. Hopefully Clowney's new deal would be front loaded, leaving more cap space to re-sign Allen/Edmunds/White. However, even with a big salary for Clowney there will be plenty of cap space to sign everyone.