The point of an offset is so that a player can't double dip.
Presumably, if Mariota is Blaine Gabbert and gets cut after 3 years, some team will take a flier and pay him a minimum wage $500,000 salary. If the Titans win and get their offset, they will have an additional $500,000 in 2018.
Right now, the Titans have the second most salary cap space in the league. $25.4 million.
They have no players due massive extensions, and if needed could save some pennies restructuring or cutting Michael Griffin, Charlie Whitehurst and Sammie Lee Hill.
The Titans do not need salary cap relief. The Titans will get minimal cap relief if they win the offset battle.
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......and also, planning for your first round pick to fail is planning to fail
Please keep reason and logic out of this. There is no place for that in this discussion.