If you're not using Ender's client, get Ender's client. Then back up your haven.jar file, and replace the one in your folder with the one in this RAR: http://www.mediafire.com/?ae5wksw4mu005yy
This is a crappy fix that loads from https://etc instead of http:/etc and just ignores all resulting errors. Everything seems to work perfectly (it even loads images you don't have in your cache), but I still recommend going back to the original haven.jar when the server is back up because the way it was fixed is guaranteed to cause other problems.
EDIT: Looks like it doesn't work 100%, but should work for most.