Secondly, some recruiters are liars who will tell you literally anything to try to get you to apply for jobs they're recruiting for. A recruiter saying MSFT stack is a dead-end just means they don't have many MSFT stack jobs on their books. If they had one they'd put you forward for it, and not tell you that they think the stack is a dead-end.
MSFT's stack is not going to disappear any time soon. It's growing just like all the rest of the industry. There's definitely no harm in learning other things, but don't write it off if you want to carry on with it either.