It's the final patch of BfA. An all out war between the Alliance and Horde, and the Alliance is winning. The final battle is taking place in Quel'thalas, near the Sunwell.
Greymane wants to destroy Sylvanas once and for all, so he takes Nathanos hostage and threatens to kill him if Sylvanas doesn't give herself up. Sylvanas without hesitation sacrifices herself for the man she loves, and the entire playerbase sees once and for all that yes, she cares about more than herself.
After Sylvanas gives herself up, Nathanos tells Greymane that if she was going down, he would too. Greymane is giddy with glee, and prepares to cast Sylvanas and Nathanos into the sunwell, for undead are destroyed by the light.
Sylvanas and Nathanos jump in together, and all the faction leaders watch--some happy, some somber, but instead of burning to a crisp, a few minutes later a high elf and a human step out. Instead of being destroyed, Sylvanas and Nathanos are brought back to life, giving them a second chance that the Lich King took from them.
duh people