Philip
Donor
The Rus remained Orthodox after 1386 and while they were in majority of the population they weren't dominant part of that population.
I am not sure what you mean by the 'dominant part of that population'. The dukes in (modern) Belarus and Ukraine remained Orthodox. It was only after the Union of Lublin (1567) that political pressure started to force conversion of the Lithuanian nobles. Of course, if the Lithuanians had been faring better against the Muscovites in the Livonian War, the Union probably would not have occurred.