Mate, if you are using MYOB Classic 19.16 (I personally use 19.17 for my Company Bees Kneez Accounting), you won't be affected. You simply keep using it offline. If you are using MYOB Classic you would have a perpetual license. If this has been lost over the years then MYOB should come to the party.
Very sad to hear about the angst and stress this has caused you!
Hopefully you have an app/icon on your desktop for MYOB Classic. If not, easily located. Again, I'm sure the moderators here can direct you to the right place to download if you don't.
Good luck!