The bug you're thinking of was Caddy would refuse to /start/ if the certificate needed renewing and Let's Encrypt was down.

They fixed that so that it has three weeks grace. Now only if you switch off the server wait until the cert has almost expired (say five days left) then switch it on, Caddy will go "eek, time to renew" and if Let's Encrypt is down it'll give up and the server doesn't start.

This means either Let's Encrypt was down for longer than a decent summer vacation or you switched off your own web site for weeks. Neither of those is a good idea.

No, Caddy never did that. Caddy never stopped serving a site that it started serving. Only by shutting down the server (or sending the appropriate signal) would it stop serving the site.