Mojang AB, a company with about 22 employees, has been sold to Microsoft for $2.5 billion. Being that the studio is based in Sweden, I would expect that it was purchased with funds that would be taxed heavily if brought back into the States, so the large sum might not feel as large to Microsoft as if they were purchasing an American company. It should be noted that they did not require that the founders, Notch, Carl, and Jakob, stay on as employees — and they aren't.
This, of course, leads to many concerns for die-hard Minecraft fans. First of all, what platforms (if any) will be deprecated? PlayStation? Mac? Linux? Java itself? Second, how will Microsoft change the franchise? Will they remain faithful? Will they reduce or remove third party content?
As for the founders? Only Notch seems to have commented on his next plans: participating in game making competitions and creating "small web experiments". Additionally, he says, "If I ever accidentally make something that seems to gain traction, I'll probably abandon it immediately." Most of his blog post references issues between Mojang and its community, regarding the EULA, server and mod monetization, possibly the CraftBucket GPL issue, and so forth. Honestly, I like the idea that Notch would spend a significant amount of free time developing web demos. I think he would contribute a lot to Web standards, especially if he is happy doing it.
As for Microsoft? Clearly they are buying Minecraft because they are running out of Halo codenames.