he seems like that kind of type who would
sacrifice everything and everyone for Mystra ... and that is certainly quite selfish thing to do.

Mystra IS Neutral
Good;
Isn't the latest iteration of her ie Midnight Lawful neutral?
No, Midnight was NG and the previous Mystra was LN who replaced CN Mystryl after the Karsus debacle. NG Mystra even tried to prevent Cyric from using magic shortly before he murdered her so unless something has changed, she probably still in NG.