Because of the nature of federation posts and comments on LemmyNSFW communities will live on basically forever. However the photos and videos will likely be lost. Some were links to external media and will stick around, some may be cached. But most photos and videos that were uploaded directly to the instance will break when the server fully goes down.

For example: [NSFW, OBVIOUSLY] !boobs@lemmynsfw.com - that link should load fine on your instance. It should look functional just with no new posts. (Note: it's actually possible to post and comment in these communities still, but only people in your instance will see it)

The images are served from links like these: (mild NSFW) https://lemmynsfw.com/pictrs/image/d50379d3-7d64-440c-bcf6-13dbf2b81c1b.webp?format=webp

The fact that the images still load is a somewhat hopeful sign. The server is still running, Lemmy just crashed. There's still time for the head admin to come back, the data still exists. This seems unlikely though as the other admin says they haven't heard from them since October.

So there's a small window to archive this stuff, if you're interested. Between now and whenever the media server crashes or gets shut off for non-payment.