While the the yoke will return to center when released, and the ailerons will return to a neutral position, the aircraft will remain in a bank until the pilot takes positive action (a reversal of the ailerons) to correct it.

Well, yes a lot of the time. I chose the Arrow specifically because it's got enough dihedral to do half-pipes on a skateboard. And I'm talking about small bank angles, not necessarily ones that would indicate a turn. (Perhaps a high-wing aircraft would have been a better example because of the pendulum effect.)

With the ailerons neutral in a shallow bank, the higher wing generates a horizontal force component. This causes the aircraft to slip. The slip alters the slipstream vector, which causes a lesser angle of attack on the upper wing and thus induces a corrective roll moment.

Now this doesn't happen on all aircraft types and at all airspeeds and air densities. This is because directional stability (chiefly the vertical stabilizer) yaws the aircraft into the new slipstream. It simply becomes a race between lateral stability and directional stability (i.e., roll moment versus yaw moment).

For fighter jets (e.g., the F-104) we introduce anhedral (the opposite of dihedral) so that the wings appear to droop. This helps induce faster roll rates. It also helps eliminate Dutch roll when the lateral stability exceeds directional stability in other aircraft. That's why we have yaw dampers on jet aircraft.

And, while in a bank if there is
no pitch up on the Arrow's stabilator the plane will enter a downward spiral

Quite true, but I hadn't intended this to be a complete flying lesson, just a discussion of the factors that affect aerodynamic stability. There's more than just computers tweaking the control surfaces 20 times a second.