Worse case, we enter the Dark Forest era for technology. Read up on this concept and apply it to the tech industry. I suspect open-source might die and everything becomes private, no more public networks, no more open access, as to assure survival. In a sense we are halfway there already as it seems the internet is starting to close down, people not posting their art and music as much anymore, not posting their knowledge for free anymore, as it might be used against them by AI (the other party in the dark forest..). Thus private authentic experiences will become more valuable.
1. The cost of running AI is dropping down to "free" - there's open weight models, open source tools, and guides on running your own if the long list of suppliers isn't good enough for your use cases.
2. Vulnerabilities have always been a risk; AI is not a panacea. The pre-AI best practices still apply. Furthermore, a huge percentage of vulnerabilities are in 3rd party tools and systems, which are systematically being scanned and fixed and/or exploited, then fixed.
You mention "the free software community" in your last sentence though - this implies the code in question is open source, so it's able to receive plenty of improvements from anyone with access to these tools.