Nope, nobody here has any idea - and GOG isn't going to tell us.
Why don't you just run your game in an Emulator and buy it here if/whenever GOG releases it?

https://archive.org/details/Legacy_of_the_Ancients_1987_Electronic_Arts_Disk_1_of_2_Side_A

https://archive.org/details/msdos_Legacy_of_the_Ancients_1989

No c64 games so far, and probably never will be unless some 3rd party releases some (legally questionable) massive c64 games collection (and even then, the 3rd party will likely skip gog, just like with most of the other such collections).

GOG doesn't sell "legally questionable" games. Nor will any other store.

Sorry, I had a longer statement about copyright terms, legality, and who gets paid and decided to drop it in favor of "(legally questionable)". That's why it took me so long to reply that there are 3 other replies ahead of me. I won't rewrite what I deleted, and will only say that "any other store" is too broad.

Maybe... but who pays for an abandonware download? (rhetorical question, not me in any case))

If the game were TRULY abandoned(as in no one was selling it or supporting it anymore) and all donations/money went mainly to the original devs/creators it would be a nice way to support them for their work.