will GOG ever have them available either as stand alone expansions or a complete compendium?

Nobody knows. Wait and see... :)

I played some parts which were released in Russia on CDs only with Russian language.
It was awesome: it is like playing HoMM 3, but this time twice as long and with more intriguing plot.
I really hope Ubisoft will allow GOG.com to publish all parts of Heroes Chronicles one day with HoMM 4 in addition.

Some time ago there was a hint from a GoG staff member that they are looking into bringing heroes chronicles here (I can't find right now that old topic). That made me very happy then, but in the meantime there was no other word about it. What worries me is that there are very few new releases from Ubisoft and the fact that HoMM IV was not released here even if it would be an obvious good old game too.
EDIT:
Found it! heroes cheronicles hint
Unfortunately there is no update on this and I doubt that GoG staff will say anything about the status of it.

One year later, we finally have Heroes Chronicles released in one complete package! :D
THANK YOU GOG!