Of course it will be up to the dev and their time/resources etc to go back and patch. That said, if this approach by Sony is what it appears to be, it should be very little effort to do so. At the very least, they could just use PSSR to take the existing quality mode and deliver it at 60fps as is, whether it's running natively at 2160p, 1440p, or something in between. The result with minimal effort should be the same quality mode running much faster. With some more effort, they could do other things to clean up the IQ (i.e. push DRS targets higher, push native internal res higher, add higher quality graphics settings) and add RT effects if desired.
I expect that we'll see some Sony 1st Party games do the extra work to deliver on the full promise of the Pro. Titles like Returnal, GT7, Spiderman 2, and Ratchet & Clank will be the poster children for the Pro (at least initially) with added and/or improved RT effects running at 60fps with fidelity mode visuals. Recent releases such as Rise of the Ronan, Stellar Blade, and Helldivers 2 should also be improved quite a bit. As for third parties, it'll depend on the amount of effort to update but Sony knows this and I suspect it will be pretty painless to update.