Don't think of it like a video game, think of it like a board game since it's modeled after a pen and paper RPG like dungeons and dragons.

You wouldn't play a board game and continue playing by yourself when your friends leave. You just don't generally play board games by yourself. If you want to play with friends, set up a "game night" a few times a week. Either get together at a table and have snacks and drinks and have a game session or set up a weekly time you can all get online at the same time to play together.

You can play this game however you want, but if you want to role play with your friends, you really should treat it like a board game and not a video game that you power through every free moment you have.

Well, that is one way to play it-

Having multiple saves lets you do both of things!

Thanks for your answer! Sorry for the late reply, but would you be so kind to go into more detail for me? Especially: How does the world work with 4 individual players? Can everyone kill every npc? Is there punishment? Can you trade between each other? Quest together or alone? What are the possibilities and limitations? Can someone screw the game over?

That is exactly how I described it to one of my friends. Yesterday I played it with my friend and after a couple of hours of gameplay it brought me back memories when I was 14 years old and playing D&D with my friends in their basement. The good old days.

You can have more than one playthrough.
One for your main friend group, and one for yourself where friends can join in to take control of your followers if they wish.

Friends can join your single player game?

Yeah this ain't diablo. You're gonna have to make a new game to play whenever you don't have your friends on.

My wife and I are going to pick this up tomorrow. Well both be playing on different PCs.

How exactly will the origin and personal stories work?

I'm in the host, will she just be a character in my story? Or will we both be playing our own stories together?

I seem to remember that the first DOS, the second player was just a party member essentially and they were going through the host players story.

Hopefully the sequel isn't like that.

All characters are saved with the host there is no moving them from game to game.

Wouldn't make any sense to do this anyway.