NPC greeting does not reset if you leave + reenter area
When you walk past an NPC so they greet you, Morrowind will reset them if you leave the area and return. They will not continue their old greeting and will instantly greet you again if you get close enough.
In OpenMW they keep their current status. After leaving and coming back, NPCs that were in the middle of greeting you will continue turning to face towards you which implies they're still greeting you. They will also not start to greet you again for a while.