A game unfinished by agreement can still have served the evening well.

Finishing is not what the evening was for. A game abandoned at half past eleven by mutual consent still did its job, which was to give four people a reason to sit at the same table and talk over a board. The result was always a pretext; the pretext worked. Treating the unfinished state as a failure imports a standard from somewhere else entirely.

Give yourself permission to stop things at the point where they stop being enjoyable. Ask the table whether anyone actually wants to see this through, and if the answer is no, put it away without ceremony and count the evening a success.