It would be legal! But it wouldn't "reconstruct" Microsoft software. The way Copilot works is just that, a copilot. It's not the pilot. It's your own fault for what you do with it, it's just giving you some help along the way.

So long as the "copilot" is a black box that no one can inspect, how is it substantially different than me creating a website with a link to download a licensing-stripped version of Microsoft office, but it only gives you a verbatim copy 1/10 times you try it?

There's an entire academic paper detailing exactly how it works. https://arxiv.org/abs/2107.03374