If you believe it is seized - it can only have a detrimental affect on the rest of the transmission.
My advice:
1. If unsure - get someone who sees a lot of them to confirm seizure
2. Buy a new one and replace immediately - OR:
3. Take off the prop shafts & VCU and run in FWD until you save up/ shop around & buy a new one.
4. Be careful if driving in two wheel drive - it will not handle as well, will be easy to wheel spin from junctions, will be no good off the black stuff
Oh and it probably won't last as long as you would like it to