The v0 Free plan has daily and monthly message limits. It sounds like you had been running into the daily limit but recently hit the monthly limit.
If you don't want to upgrade to Premium yet, all you have to do is wait for the reset date. After that you can continue from where you left off.
Vercel Firewall features can help you protect your site from unexpected high usage. Automatic DDoS Mitigation is built in, but I recommend looking into Attack Challenge Mode and WAF features if your site needs extra protection.
Chat deletion cannot be undone. There is a warning about this in the confirmation popup

You may be able to view and copy the code by clicking the "View code" link on the latest deployment in your Vercel project dashboard. Or you may be able to share the link and ask v0 to rebuild the site if your deployment is still accessible.
I hope that helps!