To Retire or Not to Retire?

I'm going to try and keep this as spoiler free as possible, but I'm facing my first major dilemma playing Gloomhaven.  When you create a character you receive a life goal.  When your life goal is completed, your character retires.  They've fulfilled their purpose in Gloomhaven, their mercenary days are over.  When a character has retired, they are done.  Yes, you can create a new character from that same class, but that specific character has lived out their adventure.

I have two characters nearing retirement, although in two completely different ways.  I've only played three characters thus far, and I've grown quite attached to them.  They're a good team.  They work well together.  If one or two of them were to retire and leave the group, how would a new member fit in?  Both of these characters are level four and one is about ready to go to level four.  They already have upgrade skills, stats, and items.  Do I want them to leave me in the lurch now?  Leave their one level one teammate all alone?

But, on the other hand, the main way to open all of those mysterious boxes and envelopes in my gigantic Gloomhaven box is to retire characters!  When these two retire I get to open an envelope and a new character.  How exciting!  What will be in that envelope?  A new mission?  A new set of rules for the world?  Treasure?  What will the new character be like?  How will they fit in with my playing style?  What skills and talents and goals will they bring with them?

This is the beauty of Gloomhaven.  I am emotionally attached to Geeple, Kezkah, and Kenna (you can hate the names, but don't make fun of them - I'm very sensitive).  They've been through some crazy adventures together.  They've taken down some big bad guys.  There is a whole lot of game left for them to explore and they won't be able to do it together.  Playing Gloomhaven you can't help but feel invested in the characters, the scenarios, the world.  I know I am.

But the question remains: to retire or not to retire?