Do you even know why Notch sold Mojang? It wasn't really about the money. It was more about Mojang turning into the very thing he didn't care for. Big corporate business. But, on a side note I think Microsoft has actually kept Mojang going. I was fully expecting them to stop all of the java development on Minecraft and make it all C code. But they have kept java development going and allow me to play using a Mojang account I purchased ages ago. So I'm not sure in this case what the gripe is about Microsoft.
Microsoft is rewriting Minecraft in C++, they're just doing so using the existing MCPE code base as a starting point. The new "Add-In" coming to all MC versions except Consoles and PC (Java) later this month is probably a first step towards the fabled "API" that Mojang mentioned years ago but have been unable to deliver on yet. The Console code is being developed by yet another company and while the "Add-In" will most likely be shared with them it's unknown when It'll appear.
At some point I can see people making a decision between the C++ version running on Windows 10 and the Java version also running on Windows 10, but that won't likely be until after both versions reach feature parity and modding is happening on both. I'm just happy I got the MCPE license with Windows 10 when it was free because I already had the Java license... The C++ version runs cleaner and faster than Java, but doesn't have mods yet, and I can use either and/or both whenever I choose.
Either way, I don't see Microsoft abandoning the Java version any time soon, if ever, as long as money keeps coming in... That's just paranoid opinion. Look around you in the forums at all the resistance to new launchers, and even the audacity that FtB would abandon version 1.7.10 packs to work on new 1.10.2 packs and you'll see what I mean