First, they probably wouldn't win. Oracle lost Google v Oracle. Wine is pretty serious about clean-room principles -- they won't accept a patch from anyone who's ever so much as looked at Microsoft-owned source code.[1] Valve has the means and motive to fight a lawsuit to the bitter end.

Second, it would be a PR disaster. "Microsoft sues to kill the Steam Deck" is an awful look for the company. Their strategy in recent years has been to say "actually we like Linux now" and play friendly to try to win developers; this would run completely counter to that. There may not be much of an immediate consequence to this, but in the long run I think we'd see developers try to reduce their reliance on Microsoft/Windows.

Third, I don't think it would actually stop the tide. Wine and Proton are a big piece of the movement away from Windows, but they're not the only piece. The legal process would take many years to play out; during that time, we'd likely see tons of movement on making it easier for developers to create native Linux builds, and perhaps even new projects that try to find other ways to do Wine-like things without actually reimplementing Win32. Losing Wine would be a huge blow, but I don't think it'd be the end of the story.

[1]: https://gitlab.winehq.org/wine/wine/-/wikis/Submitting-Patch...

> Second, it would be a PR disaster. "Microsoft sues to kill the Steam Deck" is an awful look for the company.

If the alternative is losing the entire Xbox market? Money makes people and companies do funny things.