As others have said, it'd be a shame to close the site as it's a nice little community, so I'm happy to chip in a few quid now and then to help keep the lights on.
I think continuing with the existing software would be my preferred option. Even if it has a few rough edges, it seems to be responsive, mostly solid, works well on mobile devices as well as desktop and I quite like being able to format my posts with Markdown tags (not everyone's cup of tea I know, but as an aged games programmer I find it ideal). Swapping to another platform would only introduce new issues to be resolved and seems even less viable if there's no reasonably practical way to transfer the existing content over.
Cheers,
Steve