If I can't get my hands on, say, sand blocks and water vials, will the sylestis I'm sculpting eventually disappear or disintegrate? I've poured a lot of gold, tokens, supplies, and even diamonds into trying to take care of them, and I'm starting to get worried it'll all be for nothing because I just keep running out of what I need

Not getting enrichments just means they don't complete as fast/don't progress towards the Bonuses. They won't be destroyed by anything
(even once the fest fully closes in 20 days, unless a sculpt is like, under 50% progress and has no pearl on at all, it'll be Autocompleted)

Also remember that other people can also put enrichments on them (just gotta put the url for your sandbox page in region chat or genchat so people will see they need it)

Krin also buffed the enrichment drop rate in the fest zone recently,

That's a relief, thank you! I'll see about putting it in a chat, I hadn't thought of that