thats exactly what will happen once the disc is out mate!
everything goes back to normal automatically.
depending on how far you got updating, you might have no nav operating system though(just the basic menus will show)
than you just need to use a good disc to update.
if your sure your disc is ok, give it a clean and give it another go, but remember you'll have to do the same process again if it gets stuck again!

once you get the hang of listening for the disc to stop though, its quite easy. i tried the same disc 3-4 times again and it didn't work. so i got another version of the disc and that worked.

Cheers