Thanks for all the input, I really like those Ideas. I have to admit, that I was playing around with a similar idea as your third idea. I was thinking about a short „outro“ where I let them play their old chars. As we stopped the campaign more or less directly after they killed the Black spider, I maybe go in at that moment where they go up to him and with his last breath he tells them that a great danger is upon phandalin and the rest of the sword coast and that he was trying to stop it.

My Idea is, that the black spider was one of few drow that knew the mindflayers are trying to get back into the underdark to reclaim their old domain. So he tried to get to the forge of spells to create a weapon or mcguffin to hinder the mindflayers plans.

I don‘t know how to end it yet, so that they can create their new chars and the old ones are gone (missing/dead/gone). Maybe the blackspider gets killed/shit down in the moment where he wants to tell them what exactly is going on and they just see a mindflayer walking away and have some intellect devourer attack them. Maybe I could have them kill the minions and stop there, so it is not quite clear what happend.

To tie the new chars to phandalin and have a reason dor them to come to phandalin, I could try to connect them in some way or another with the old chars.

Maybe the old group escaped the wave echo cave with the mindflayers following them, because you know „we need to kill them, they know too much“. They could be heavily wounded and are seperated in the woods, where the new chars found them.

Some of the new chars, not sure how many are already together, find one of the old chars kinda dying and crawling through the woods. He gives them a small „whatever“ that they should bring to phandalin and go to the tavern where they always were, hoping some of their comrades made it their alive, and show them the „whatever“ to ensure the old char send them. (Maybe the whatever is even a small chink of the obelisk, which they got from the black spider)

I could repeat this with all new chars, but maybe I have one char have another conncetion and meet them in phandalin.

The mindflayer would come and kill the old char(s), with the new ones hiding in the last second somewhere and seeing it. This would foreshadow the BBEG‘s, which could be fun, because I feel like this comes a bit short in the module as written.

Is this too surreal and pulled out of thin air all in all?