I was reading a bit about some of the future quests and found out that there are specific companions that will no longer follow you after certain quests (the one I'm thinking of specifically dies). This made me wonder, what other situations will you run into where companions will not/can not follow you? The reason I'm asking is I'd really like to get all the companion perks, but also want to beat the main storyline. I wanted to be sure to get the ones now that I won't be able to snag later.
Thanks!