Technically, I wasn't near the end of
Heroes of Might and Magic III when I gave up the first time I attempted the campaign. And I did go back some years later, which was also partly how I stumbled upon GOG.
It sort of has a four-part campaign, each with a character to develop while progressing through the story. After going through all of them, there is supposed to be more to the story, and the development of each character plays part in that.
The start screen allows starting any part of the campaign and doing them in any order, as the screen is essentilally split into quadrants for choosing one or the other. It is possible to save progress during each part, so I chose one, completed it, saved my progress and came back later.
Then a second one, saved, came back later. Third, same thing. And the fourth.
Nothing had changed on the start screen.
I read the manual again, and tried to figure out how to proceed further. Yes, the game is that old, that it actually had a manual (and definitely not renamed as an optional "hintbook" bonus item at an exorbitant additional cost like they do nowadays). Turns out I had inadvertently created four beginnings, because I didn't LOAD my saved progress before choosing another part of the campaign.
It just wasn't obvious to me, because I had remembered from the manual the progress would be combined. And maybe because I was used to Nintendo consoles where sometimes the progress affected the whole cartridge (f.e. multiplayer bonuses for StarFox 64), or else it clearly listed all prior saves along with a "New game" selection.
I sulked because I wanted the familiarity of my progress through all four parts I had completed, I wanted to continue with the story in mind I had pieced together from all of that. I toyed with the idea of picking one of the four and continuing, maybe for each one. But I knew I would forget where I left off at with the others, and I knew I would get the different results confused along the way. So, instead, I switched to the plethora of individual maps and eventually stopped sulking about it as much.
About ten years later I discover GOG and found it again. I recalled how much I liked it and that I never finished the campaign. So I bought it, loved the nostalgia, played some individual maps to refresh myself with the gameplay, then dived into the campaign to finally complete it.
But...
I did the exact same thing again. Inadvertantly created four beginnings because I didn't think to load my saved progress. Then I remembered that had happened to me the first time, too. And I sulked again, but in a manner fitting with it being the exact same thing that had happened a decade eariler. And then I switched to the individual maps to relieve my sulking, again.
I have yet to try the campaign again, but I am pretty sure I will remember next time, when priorities and opportunity work out again. Really, I remind myself every time I think about the game, and that happens about every time I load GOG in the web browser because it is usually in the top ten games (was #1 forever, until maybe last year?). Just gotta set up a system that can support the installation. Someday again.