[Luvian]

There is no rule for soloing, you do what you want. Personally, when there is a central plot point centered around an NPC, or when refusing an npc break the storyline and roleplaying, I take him along and then drop him after the event.

Just like Imoen. If you are good, you would most likely not abandon her there alone, she is your childood friend. So I take her until I leave the dungeon. I just tell her. "Stay behind, I'll call you when the way is clear".

When I look back on my game, I want to remember my pc as the guy who traveled the sword coast helping people in need, not the anti-social guy who rejected everyone.

Don't let people dictate how you should play. This is all about having fun. If a player-made rule seem silly or anoying, then don't use it.