Chances are, the obligatory jokes about disturbing online subcultures aside, LiveJournal won't disappear overnight. For one, the cuts are in the US office, and LiveJournal is now Russian-owned, and is much bigger in Russia (in America, the typical LiveJournal user is a thirtysomething goth-scene veteran with an IT job, whereas in Russia, it's a mainstream media site). Given that most of the money and ad revenue come from the Russian operation, it presumably won't cost them much to keep running an English-localised rump site on the same servers.
In any case, I hope LiveJournal survives, because it has one thing none of the other sites have: no, not Harry Potter slash fiction; fine-grained social-network-based access control, i.e., the means to specify that posts are not just friends-only but only accessible to a subset of friends. Which might sound like a symptom of some kind of geek social neurosis, but is actually useful. (Consider, for example, a Facebook friends list, containing everyone from coworkers to family members to people you met at a party or festival; as on Facebook, you can't control who can read a posted item (it's all your friends or no-one), there are a lot of things you cannot or should not post; from boasting about faking illness to planning surprise parties for contacts, to discussing personal situations, so your Facebook stream becomes a stream of lowest-common-denominator banalities.) Something with Facebook-level usability and LiveJournal-level access control would actually be useful; maybe once the world emerges from the New Depression, someone will write something like that?