I'm currently planing a game idea, a coop crew based space shooter, where the focus is set heavily on the coop part. Depending what role you have, complexity varies: Gunners and Pilots are pretty easy, while engineers and doctors are way more complex. Crews may contain two to maybe 8 people.
This is only an example for a coop game, while there are many others out there.
But my thinking was, what about the people that want to play alone? Or in less big crews on bigger ships.
As I said, there are many other games out there that try to solve that problem. Lovers in a difficult space time has an A.I. that is basically a commendable token, Guns of Icarus has simple A.I. dudes, while Endless Dungeon let's you play all of your characters RTS style.
In my case, writing an A.I. that does everything is problematic. Gunner and Pilot would be possible, but Engineer is to complex. And making the A.I. simply perfect could and would break the gameplay. Making them less reliable would force me to implement some sort of crew management just for Single-player. Doable but not the focus.
My question is: What other options for a coop game are there to make it playable and enjoyable for Single-player?
I'm looking for answers not just fitting for my game, but coop games in general.