Will this site ever die? If it does... alternatives?

Not as long as lozer keeps getting his tendies.

I'd certainly hope not! IMO Gelbooru will never truly die unless someone or something forces its servers down. However, never say never. A year or two ago, there was a massive scare involving the famed exhentai site over legal bullshit. It is good to have (and contribute) to backup websites.

The good news is that there are indeed lots of alternatives. Personally, I have experience with two: Sankakucomplex and rule34. They have their ups and downs. I like Sankakucomplex a lot. It is actually larger than Gelbooru and pretty technically sophisticated. However, there is an upload limit on new users, and site support + community engagement feel a little limited. (Also, mind the paywall if you happen to like popular stuff... which fortunately I don't.) rule34 is sort of a wild west in my view for better or worse, but it is also small, particularly when it comes to many more niche tags and fandoms.

Ultimately, I think the best thing is to cross-upload your favorite content to ensure its immortality on the interwebs.

It's been up for over a decade and admins are still quite active.
There is little reason for it to go down.

R34 really, truly, needs to get better with tagging. I understand that some of the tags we have here are kind of... eh, but what they do is just series, character and maybe artist. If even that.

Rule34,xxx (I don't think I am allowed to actually put the . in there) has more tagging flexibility than that paheal dump, but still, the same issue applies. Nobody can tag for crap. And this matters a lot if you are like me, and you only get off on one, very specific fetish. Also, there doesn't appear to be a way to easily check if an image you want to upload already exists, which sucks if you are obsessive over keeping your favorite content nice and tidy. *(Ironically Sankakucomplex makes it very easy to scan for duplicates, but the problem there is that the mods don't ever do anything about flagged dupes)

Rule34 thingy also seems to not allow loli and shota according to a quick check of the rules disallowing drawings of underage looking characters... so a fuckton of content couldn't be ported over.

Though they do seem to draw a seemingly arbitrary line at enforcement as some of the "totally not loli" pics are very visibly young looking to the point where I question the logic behind their nonsense. But ehhh... that sort of stuff has always been arbitrarily decided by people anyway...

There's lolibooru for loli stuff as well.