That is the only likely future ahead. BS is growing so fast that there's no way they can sustain this growth even if they add ads. The only path forward is selling out. I think Microsoft might be interested in finally owning a popular social media site.
Won't happen. Not necessarily the them not buying it part, but it staying popular at all. No site/program is too big for Microsoft to torpedo. Skype used to be the verb for voice calls before they got their hands on it.
I didn't say MS would make it successful. They would definitely buy it, add Minecraft to it, integrate teams, then forget they bought it, neglect it, and leave it more broken than when they found it.