Licenses are contracts. It is impossible to retract without just cause and cannot be done on a whim or because a party thinks they will profit more without it. That would be frivolous and thrown out in court.
And TC and Diwan would not profit more even if they wanted out (which they don't). That would mean licensing to someone else and starting over. Slower to clinicals, slower to commercial release, slower to profits. Just not in their interest to do so.
And they'd have to convince someone to buy the license that they are trustworthy, just after they screwed their last partner - in this highly speculative (ridiculous) scenario.
[Edit] And all the while the value of the license goes down as the patents get closer to expiry. Time is money very literally in this case.
[Edit2] And Diwan and TC still own huge amounts of NNVC. Any new license agreement would have to exceed the present worth and opportunity worth now held in NNVC to be worthwhile overall.
None of this adds up as a legit threat to present licensing.