Good point about the franchise tag there ^^^^. If you signed him to a multi-year deal, you still have to figure the signing bonus. I just don't see how you could avoid keeping him and paying him less than 15 million dollars THIS YEAR, even if the signing bonus doesn't count against the cap. The signing bonus is really the only guaranteed money the player gets beyond the first year salary. In year 2 the player could get cut and the rest of that contract is just toilet paper to wipe his buttocks with.
If you let Long walk, you let him walk because you truly don't believe he can play well anymore. He wouldn't take a one year deal so a huge signing bonus would be the discussion.