I have a very restrictive ISP, for reasons I won't go into. I think what happened is that the first time I visited the site after the SSL cert expired, it got added to the ISPs block list. From then on, regardless of whether I used http or https, I'd get redirected to a page saying the site could not be accessed. This was not at the browser level. So I need a VPN to get around the ISPs block.
All that said, for new people coming along, they're likely to just see the page get blocked by their browser, and not knowing any better are likely to not come back.