TL;DR: A Game of Thrones mod for Crusader Kings 2, Dance of the Dragons bookmark. Basic premise this save was to run the observe command and play as whoever wins the Dance itself.

In the end:

• Aegon II died early on in the war at the hands of a random Reachman commander
• Rhaenyra would be murdered on the orders of her one-time champion Criston Cole
• Aegon II's son Jaehaerys would inherit after his daddy's death until he was captured in 130 AC
• Leaving us somewhat similarly like the books: The Greens technically winning the war towards the end, but with one of the Blacks ending up on the Iron Throne

This person in question is Jacaerys I Targaryen....or Velaryon as he was upon birth....or Strong/Waters if you believe the (well-founded) rumors of his parentage.

As of the fifth month of 143 AC, he has finished uniting the Seven Kingdoms, bringing Dorne into the fray by 135 AC. Pentos would technically also join upon noting that "I have dragons, you don't, be a good chap and bend the knee now". Book Aegon III is a septon, book Viserys II is the Archon of a now-freed Pentos.

As for marriage and succession, Jace is married to his cousin Rhaena, with whom he has four daughters to date:

• Alyssa, heiress presumptive, 9
• Leaysa, 7
• Vaena, 4
• Aerea, newborn
• Even if Jace was to have a son, Alyssa would still be heir owing to the mod's mechanics having gender-blind/Dornish succession upon winning as Rhaenyra or friends (not sure to if this applies to all five of her kids or just the "Velaryon" ones)