I am not a lawyer, but I imagine a lawyer would find it alright if they just restore the missing notice. I do not imagine there is much else that can be done here since he cannot really claim to have been significantly damaged by the absence of a single line, but these matters are best discussed with attorneys.
IANAL but my understanding from floating around open source licensing circles is that you'd have a hard time with the judge if you didn't just ask for the license to be put back as step 1. Microsoft willingly not restoring the license would be more problematic.
The forgiveness clause in GPL 3 is as much an acknowledgement of actual reality than anything else.
I imagine a lawyer sending them a settlement offer for the blatant copyright violation they committed would get them to settle for a five-digit amount, since just the cost of discovery (and potentially having the "let's just fork it" dirty email laundry aired in public court) would be much higher.
