Dave,
I was also a Worldnet customer, and got the same notice. Fortunately I had already migrated most of my stuff to other servers. But I did notice that they provide guidance for downloading websites to your hardrive, so that you can eventually upload them to a new server if and when you find one. I had better stop here, because being a computer dinosaur I am hardly one to give anyone advice on this sort of thing. But given all the work you have put into your site, it is worth considering.
JBWX