The first 2 Thief games ate interesting:. They still have a relatively active community, but the executable is hard to run. Then most of the source code leaked, and new releases started from that.
The result is a zombie game. The fans won't let it die, but the copyright limbo won't let it live.
Transport tycoon had a bit of the same, but managed to grow out of it by piece by piece replacement, with ttdpatch, openttd and fully new graphics as important phases. So it is possible to slowly escape this fate if the fanbase is interested enough. But it is a hard, multi decade effort.
The result is a zombie game. The fans won't let it die, but the copyright limbo won't let it live.
Transport tycoon had a bit of the same, but managed to grow out of it by piece by piece replacement, with ttdpatch, openttd and fully new graphics as important phases. So it is possible to slowly escape this fate if the fanbase is interested enough. But it is a hard, multi decade effort.