I had rebooted my router due to a few other things not working right so you could've just tried right when it was offline.
But I've just rebooted the Minecraft computer, it was probably due a reboot.
I don't remember for sure, but I think I got the offline thing twice, about ten minutes apart.
Anyway, just gave it a quick try now and it appears to be working fine, but I have stuff to do so can't play. :(