Roll stability
Letīs look at the sequence starting from roll.
1) Airplane rolls. When not stalled, it has roll stability - one wing dropping has higher angle of attack, more lift - that stops the fall of the wing. But does not yet reverse it - a rapidly rising wing would lose angle of attack and therefore lift.
2) With airplane banked, part of the lift works sidewards - the plane starts yawing in the turn
3) Yawing means the outer, upper wing has higher airspeed than the inner and lower wing. Not sure about how the angles of attack compare... anyway, this may mean more lift on the upper wing, causing overbanking tendency, which would mean spiral instability and drive the plane into a graveyard spiral.
Now, what exactly will the fin and wing dihedral do to stop the spiral dive and return the plane - perhaps into a Dutch roll?