I sympathize with the operators of these forums of course -- the UK Online Safety Act is poorly conceived.
HOWEVER.
Deleting their forums?
"The act will require a vast amount of work to be done on behalf of the Forums and there is no-one left with the availability to do it." [1]
This is a false dichotomy. Put Cloudflare in front of the site, block UK traffic [2], and you're done. 5 minute job.