The Philosophy of Heroes of Might and Magic.

We can consider, for example, its influence on the social development of the human race, which could not have happened. Right, XEL?

Hmm, why couldn't it have happened? It still influenced Erathia, winning two of the most important wars in its history and ruling well for 4 years.

If Sandro hadn't existed, what would have happened to the world, and what path would it have taken?

1. King Nicholas Gryphonheart would not have died.
2. There would have been no War of the Restoration in Erathia.
3. Jelu would not have become the commander of the Forest Guard.
4. Phineas Vilmar Deathbell would not have become the king of the Necromancer land of Deia.
5. Archibald would not have become the ruler of Deia.
6. The Reckoning would not have happened.

P.S.: And why consider the game mechanics separately from the plot? Why not combine them organically?

For a number of reasons.
In the game mechanics, resurrection is possible; in the plot, it is a unique case. This refers to a full-fledged resurrection, not necromancy.
In the game mechanics, you have to pay money for any creature. I think this is clear. Angels, demons, dragons, skeletons, all are hired for money. From a plot perspective, this is nonsense.
In the game mechanics, creating Armageddon in Steadwick or Free Haven does not affect the plot in any way, and Armageddon itself is an extremely powerful and rare spell in the plot.
In the game mechanics, blasters are far from the strongest weapon in the game. In the plot, however, it kills much faster than almost all types of magic and weapons.
In the game mechanics, you can easily mow down Devil-Krigans with Dark Magic. In the plot, they are resistant to many means of destruction on the planet, and the main characters destroy them with blasters.
In the game mechanics, there is a spell called "Dimensional Door," which allows teleportation.
In the plot, such cases of mass teleportation over huge distances are rarely recorded.
In the game mechanics, a Barbarian can reach the fifth level of Wisdom and Intelligence. This will not affect the plot at all.
The list can go on.