So far we know ALL npcs import into the start. Then some of them of them leave near the start. Im pretty sure theyve confirmed the following can come with you: Neera, Rasaad, Dorn, Khalid, Jaheira, Minsc, Dynaheir, Edwin and Safana. On the whole it looks like party members in BG2 will stay with you and others will leave at various points.
I never got the impression it was more than a few weeks. The BG II portrait artist also seemed to like scars in general, most characters have one or two on their faces. It might not even have anything to do with the plot, we'll have to see.
Comments
https://forums.beamdog.com/discussion/48243/list-of-known-continuing-companions-into-sod/p1
Would be nice for Beamdog to let us know but i cant see that happening any time soon.. maybe the next dev stream if we are lucky.