Why not fork it? The usual reason to upstream patches (aside from charity) is to offload the work of integrating them with future upstream changes. If upstream is not making changes anymore, what’s the problem?
Perhaps the concern in forking it would be that the group that creates the fork now has the responsibility of maintaining another project, on top of the project(s) they already maintain.
A part of me thinks that sounds like a fun retirement project, to become the primary maintainer of a useful but unglamorous OSS project; another part of me, looking at how my predecessors (already-retired programmers) apparently disagree, suspect that by the time I retire I'll either not want to deal with the burden, or have more fun things to spend my time on.