Re: They already have a legal route
Microsoft employees based in Ireland cannot comply, Microsoft employees based in the US can. Even if there were anything in Irish law to prevent Microsoft's US employees handing that data over if they have access then there's no way to enforce it.
Microsoft may well decide not to give any Microsoft Ireland employees permission to grant or revoke access. That would keep their European employees safe if the Irish authorities ever decided to stop looking the other way.
If the Supreme Court follows to same line of reasoning that it did with the border restrictions (remember three - including Trump's puppet - voted for unrestrained executive authority) then this is unlikely to go well for Microsoft or any of us.