Evidently NBC is unfamiliar with the concept of fulfilling a contract.
Conan quit by not taking his Tonight show to 12:05 so he just gets his parachute.
That’s what the contract pays if he stays through the end. They probably negotiated a breach payment (liquidated damages, if you will) and that’s where something less than $70M comes from. If they breach, he gets that payment, and can be on the air in some period of time at an alternate venue. So, given that he can be earning another income stream, you would expect the breach obligation to be less than the remaining term times the negotiated rate.
That said - NBC is looking very stupid. Unless they think they have a “New Coke” kind of promotion masquerading as a controversy (and I don’t see it) this is really dumb.