Lithuania would convert in the late 13th century or early 14th. If Catholics surround them on all sides, the OTL dilemma between Catholicism and Orthodoxy is replaced by a weak Catholicism-paganism dilemma, which Christianity would win easily on practical reasons alone.
However, a catholic Rus would either butterfly away or dramatically affect the Baltic Crusades, yielding a yet another big change. Maybe Lithuania never ends up expanding east and instead gobbles up the other Baltic tribes (which, if the Baltic crusades don't happen, would be ripe for taking), becoming a secondary power by the Baltic sea and later adopting Christianity.
The formation of the PLC is not at all ordained in this scenario, and it's very likely that the specific circumstances needed for the Union of Krewo and beyond would never arise.