A seemingly simple question, but valid nonetheless.
What exactly happens when a browser which does not support SNI attempts to visit a site configured to force SSL via SNI.
It will probably connect to the default SSL virtual host. In other words, the same site you'd see if you connect using the IP:
It won't be able to load the website, that's for sure. Which is why no large sites will move to SNI-hosted HTTPS sites anytime soon. IE6 and IE7 in XP appear to be the largest old browsers that don't support SNI.
If you can get a hold of a non-SNI supporting browsers, you can see what happens by going to https://alice.sni.velox.ch/
It also appears to matter which server software you are using. With Apache, browsers without SNI support will just get the first configured website (and a hostname mismatch warning probably).