Free software might collapse, but open source certainly would not especially since so much of it is under MIT and similar licenses which already allow anyone to do pretty much whatever with that code.
That being said, right to repair goes hand in hand with the abolition of IP to resolve these edge cases. The problem of not providing the manual to your distributed invention goes far beyond just intellectual property, and is largely an independent issue, but good right to repair legislation is all encompassing, and is a consumer protection that naturally fits with IP-less software as well.
I don't know about that. Most significant software packages require ongoing maintenance (bug fixes, security patches, compatibility with other software) and add new features over time. A one-time leak certainly would be damaging but not necessarily fatal since most businesses want to have assured support and upgrades.
And not to get sued into the ground.
After the leak, anyone can.
Prices would adapt to the reality, and the original vendor would have a hard time demanding the rates they are used to when suddenly faced with competition. Especially competition that kept changes open, which instills more confidence in consumers of the software.