They are not vital, but you will miss quests from (in no particular order): Jaheira, Keldorn, Mazzy, Valygar, Nalia, Anomen, Cernd, Jan, Korgan. I don't think I've missed anybody. Most quests, with the exception of Jaheira, are quite short. Romances are not an issue if you don't intend to have any Bioware npcs. No areas, except certain npc residences, are inaccessible, but some will be missing content.