So Microsoft employees must choose between flying to Ireland, breaking the law and facing possible arrest or losing the case in the US. They could ask their Irish subsidiary for the data but I somehow doubt any of those people will be willing to go to jail to satisfy a US court that has no jurisdiction over them.
There is a question in "breaking the law and facing possible arrest[.]" First, there has been no indication that Irish laws will be broken. Second, there is no reason to believe there would be an arrest if they were broken by a corporation acting in good faith to comply with the laws of another country. Third, most laws around data storage privacy have an exception for disclosure pursuant to a valid court order or warrant. Fourth, it is a multibillion dollar company more likely to face a fine than to have its employees arrested. Fifth, nobody needs to *fly to ireland* unless Microsoft wants them too--MSFT has people there. And flying to Ireland is not a big deal for an employee of a multibillion dollar corporation.
The messed up thing here is *NOT* requiring MSFT to turn over their data where electrons are located in Dublin. It's the scope of material they can get without a showing of probable cause under the 1986 law that determines privacy for email.