I remember that the son of Mindaugas is a devout Orthodox Christian but he is very religious and uninterested in ruling Lithuania, what if he wasn't like that and promoted Orthodoxy in Lithuania what would had happened to Lithuania?
Poland is still divided on 1270's actually.You don't need an Orthodox Great Horde, what you need is a weak Poland and the Knights as the foremost menace.
Staying Orthodox and gaining allies among Russian principalities is more attractive then.
But what if he was able to pull a Jogaila and put a Russian principality in union with Lithuania.Civil war.
It's not that hard to predict. Vaisvilkas, son of Mindaugas, abdicated after revenging himself on his father's killers. He abdicated in favor of his brother-in-law, Svarnas. Svarnas would have been Christian, too, since he was a member of the ruling family of Halych, a Rus principality. He only ruled for a couple of years, because he couldn't hold on to power in the face of a pagan rising led by his successor, Traidenis.
It's hard to see thinks going any better for Vaisvilkas if he tried to keep the throne himself.