Questions about the Heroes 4 map editor.

- Is it possible to make a hero disappear from the party at a certain point?

As far as I know, no.

- Is it possible to make a hero disappear from the map? You approach him, a dialogue appears, and after the "conversation," the hero disappears.

Theoretically, it is possible, but only if the hero is alone. The main thing is to enclose the area on all sides (trees, stones, etc.) and place a gate, I don't remember what they are called, which only allows passage under a certain condition (script: SPECIFIC HERO - HERO'S NAME - THIS ARMY). After the "conversation" (script: SEQUENCE - CHANGE PLAYER TO - NO PLAYER, GIVE THE 5TH-LEVEL STEALTH SKILL, REDUCE MOVEMENT BY 50 PERMANENTLY (if the player only has this hero on the adventure map, after changing the color, they will be able to control a neutral color; the movement reduction is necessary so that the hero does not leave the enclosed area, and I think you can guess what the stealth is for)).
Theoretically, it should all work, but I can't say anything about practice - I have nowhere to test it.