I have a 25 sized plane with only ailerons and elevator.

A vertical stab helps the plane track straight and provides yaw stability.

Would one fly without? Yes. But it would be a terrible pattern plane, and a terrible 3D plane where you often use lots of rudder.

Vertical stabs also help a lot in spin recovery. But look at flying wings, most don't have vert stabs. But a lot of them do for yaw stability.

Anything will fly with a big enough engine.