The instant cascading worldwide deletion upon closing or deleting a subscription sounds like a recipe for disaster. Why not mark it for deletion and delete say... a day or a week later?
Treat this as person's own contribution. If the quality is bad, means the person has allowed it, or the person's quality of work is bad, and it doesn't matter whether they produced it or AI did. So in both cases they'd deserve a rejection of their PR. The only downside is that it takes away precious reviewer energy and time.
Since Doom renders the image with vertical columns of pixels (floor, lower wall, portal if exists continues rendering the other sector, then upper wall then ceiling) and since browsers are very good at drawing the sprites out of larger textures... You could send vertical divs shaded with the sector light level and picking the correct textures. Instead of hundreds per column you will have like 5 divs on average per column and they will be textured shaded and scaled by the browser?