Earlier quoted context omitted.
"Future career prospects"... well, that depends. What does he want that future career to be? More work as a peon in other giant corporations, climbing the ladder to middle management? That sort of thing can lead to looking back twenty years, thinking, "Why on Earth did I waste all that time?" Believe me, I know. I often quote Mr. Morden from Babylon 5 , asking "What do you want?" Most people don't have the nerve to e…
You aren't cast into one thing for life unless you choose to be. I'm sure startups would be happy to hire someone with Microsoft experience. Out of people I know working for startup type companies, one cut his teeth building enterprise Java stuff at a bank and the other spent time in the military.
More importantly, a lot of them would be happy to hire someone with Microsoft connections.