It’s true that it’s unhelpful to demand money from the user who wants their posts deleted, but if they were a regular is there any way you could ask for something towards the costs? Especially if you mention how in dire straits the site already is. Surely they’re not totally heartless.
It’s rubbish to think the whole site and these forums might end as a result of one person, really. But they are within their rights to request it I guess