If it's the full, genuine GTA5 source code, the community could benefit from it. Tremendously. It means bugfixes where none happened, extensions where none happened, modifications where none happened, and support when none is provided anymore (sure, R* has a pretty good track record in that regard, but still).
It's not legal, but pretending no one will benefit from it or that R* is now leaking billions (because that's what ruining projects is about here) on a decade-old game is disingenuous.
This is the way.