Yeah they'd probably run the same .exe files from their steam folders. And to buy new games, they'd go where games are sold. Which would be the Microsoft store. Which would be extremely beneficial for Microsoft.
There would be no update mechanism meaning games would get out of date with no way to apply patches, and no steam api for multiplayer games meaning nothing would work online.
You seem to not really know much about the subject so I will stop debating with you here.
