I am not going to go through a map of events and draw out what affects what. But, in theory, a completely unique run involves a party, set of mechanics, and event order which is never repeated. In theory, at minimum:
-Party 1 (Dark Urge plus 3 companions), Event Order 1, Combat-oriented, Evil-aligned.
-Party 2 (Tav plus 3 companions), Event Order 2, Dialogue-oriented, Good-aligned.
-Party 3 (Origin plus 3 companions), Event Order 3, Stealth-oriented, Neutral-aligned.
-Party 4 (Origin Lone Wolf), Event Order 4, Mixed Tactics with Prior Event Exploitation, Various-Aligned.
Glad you're onboard with the math approach. Scattershot thoughts:
1. I hadn't though of a Lone Wolf run, but it's a good idea. It goes to show there might be more unique ways to play than appears at first blush.
2. That run brings the count of companions to 11. There has to be a duplicate between the 4 parties.
3. I'd count a Dark Urge kill everyone Lone wolf run as unique, though you might not under your rules (conflict with Party 1).
4. You might get more different parties with hirelings.
- Tav, Astarion, Halsin, Merc1
- Dark Urge, Gale, Jaheira, Merc2
- Karlach (origin), Lae'zel, Minsc, Merc3
- Shadowheart (origin), Wyll, Minthara, Merc4
- Dark Urge solo murder hobo (presumably the other Dark Urge run would be good aligned)
5. The number of companions and "alignements" clearly limits the number of unique combinations. But I wouldn't try to draw the map of events either, that thing must be huge! I think there will be many more ways to traverse the game that will feel unique enough than a list of 4 party options could reveal.