It doesn't matter if they're not selling as much as they used to (and just for the record, their sale never really dropped, up until a few weeks ago GTA V was still the top seller on Steam) because anyone can still review at any time. You can even change your review and rating at any time, which was actually the whole point of adding an additional rating last year: overall and recent. Because game can evolve and the overall rating may not be indicative anymore of the state of the game at the current time, that's why Steam allows you to change your review.
So much this. Seriously. While there are good reasons to be pissed off by Take 2's move, there is no reason to freak out. You can still use OpenIV by disregarding the uninstall invite, you can still use mods, you can still play LSPDFR. The worst that can happen is being stuck with the current game version (that's why you make sure to back up the important game files) and that's not the end of the world. People can still create the most awesome mods with the current version, the LSPDFR team even just stated that they are testing a new version...