Can I stop migration from my PC to new MacBook Pro without loosing what has already migrated?
Since Migration Assistant tool has no pause / suspend button (and in the past when it did, it deleted the files and cleaned up if my memory is correct) you might get unexpected results on one or more files if you abort things.


Cancelled wireless Migration Assistant... best way to start over?
iMac-to-iMac Migration was interrupted; Now, source iMac is reading as 0.0GB
Migration Assistant moved files to inaccesible new account, how to get to my old files?


As you can see, even Mac to Mac transfers which are supposed to survive a disconnect are sometimes not resilient. I believe a PC to Mac transfer is much simpler and akin to copying files, so you might only have one file that got corrupted if you interrupt things.

If you abort the transfer, all the files will be copied, but there is no guarantee they left a workable user account. In almost all cases, you can then log in and get to the files that have transferred, but you will want to clean things up / hand move things to the correct location.

Since Migration Assistant doesn't move an entire PC user over, you might be fine with what transferred, but you have no way of knowing what has been transferred without puling the plug (so to speak).