Again, exclusives have a monetary value. They could of negotiated it into it being 'The Agent', but the deal could just as easily be renegotiated to be a decade's worth of exclusive marketing rights on all Rockstar releases, or exclusive DLC for the next 2 or 3 Rockstar Games, or whatever else that is decided upon between Sony & R*.
Personally, I don't see them pulling the trigger on their contract for RDR2, but if Sony finally understands that the dev effort behind Agent has fully stalled, I could see them trying to renegotiate for some other form of compensation. I mean, last estimate for how much that deal came out to was over $50 million worth of funding, so its not like its a small bit of chump change Sony lost & is looking to regain from the LA Noire deal.