As long as:
1) people want to socialize freely (as well as privately) with each other in an online rapid medium,
2) the online forum is incentivized to make money, and
3) that same forum / business doesn't want the burden of regulating people's speech and behavior
then some Facebook analogue will take its place no matter where people go.
Right now it seems we can only choose to have 2 out of the 3.