My novice opinion is Sprint has been going after the lender approvals of later to try to cover the credit aspects of the agreement. If DOJ then approves, T-Mobile may owe them $600 Million, but Sprint would have to do whatever T-Mobile decides: sue as is, sue and start merger in other states, drop merger.
Network Joint Venture with separate marketing may make more sense, but the problem is how the Sprint debt is handled.
I can also see multiple ways this gets played no matter what happens, all depending on the larger players. Softbank might even accept Sprint being split apart and sold to multiple entities if their dream of proper scale through a T-Mobile merger can not be realized. Failure of the merger does not guarantee four national wireless competitors. Wireless may move beyond that definition.