I think it's possible to retain the origin characters as "legends" who had a pivotal role in the story, and then the DM can decide what part that was. That way you can have the best of both worlds.
The problem being that in some stories some characters were never in the party or got killed in the beginning.
I think the way BG3 implemented Jaheira and Minsc is a good way to acknowledge a past adventure without making anything "canon" about it (although I will admit I didn't play BG or BG2, was it possible to end those campaigns with them dead?). "Legends" indeed. You can ask, but they won't tell you any details apart from the general who fought who. (Definitely won't gossip with you about romances in their old party!)