After update it was gone from my choices, repeated attempts to reload, uninstall, reinstall, all say disk error

I'm not sure what update you are talking about, but my copies of HOMM2 version 1.0 (2 PCs) all stopped working today (I'm pretty sure I played it yesterday, but I may not have; definitely played it two days ago.); the DosBox MultiPlayer selection menu comes up, but after selecting single player, that window closes and nothing happens; no game.

I've tried the repair installation trick, and deinstalling and reinstalling, no joy.

My copy of Master of Magic, also a DOS game, works just fine. So it's not a DosBox issue.

I had been concerned that it was an incompatibility with Windows 10 Professional (x64) Version 1903 (build 18875.1000) prerelease 190405-1518, but I realize that I ran HOMM2 after installing that with no problems.

GOG did update when I loaded it to search for answers, but the problem began prior to GOG updating; I don't normally have GOG loading at boot, so it had been some time since it had updated. As I use the Multiplayer option to start HOMM2, it doesn't bring GOG up each time I play.

Attempting to run HOMM2 straight, without going through the multiplayer selection, did bring up GOG, but it still failed to run after selecting 1 in the DosBox selection screen.

So my problems may or may not be the same as yours as I didn't see any disk error messages, but the timing is sure suspicious.

Note: normally, if you are getting disk error messages, I'd suggest using a utility to check the integrity of the disk to make sure it wasn't starting to die on you.

ETA: Now, I happen to have one PC where I still have HOMM2 version 2.1.0.29 installed; it hasn't connected to GOG to "update" to the latest version yet, so it didn't get rolled back like everyone else has. _That_ copy runs just fine. I hadn't checked that PC prior to making the initial post, and hadn't realized it was still running the actual updated version, rather than suffering from GOG jerking us around by rolling back to version 1.0

ETA 2: Searching my various computers, I found a downloaded offline installation file for HOMM2 v. 2.1.0.29... and when I install that, it runs just fine on the other computers. So... it looks like something is broken with HOMM2 v. 1.0 and the latest updates.