I don't see how Microsoft buying out Linux Mint would change anything. Linux Mint is just a configuration skin on top of Ubuntu/Debian and is fully open source. If Microsoft bought out the debeloper someone else can just take the code that exists currently and create "Linux Hibiscus" and people can just swap over by changing one repo config file.

General turmoil in an important project like Linux Mint will work to Microsoft's advantage. It will usually lead to developers and users leaving preventing Linux Mint from becoming a desktop Linux rallying point.