(a) the ball has naught to do with sideslip .. symmetric or asymmetric .. or, indeed, gliding ... (other than incidentally ..)
(b) after the failure has been sorted out, there is a lateral force (due to the rudder angle) .. which causes a lateral acceleration and velocity to balance out the unbalanced force .. hence, a resulting sideslip angle
(c) a touch of bank the other way (2-3 deg) cancels out the sideslip in (b)
Try a few searches as this topic has been done to death in the past ..
This one is a good place to start ... be aware that Milt is a retired, very experienced test pilot and is stirring the pot masterfully in this thread ... he sucked me in well and truly for a while until I twigged to his gameplan. Amongst his acknowledged skills is included telling wonderfully entertaining tales over dinner with a wine or two ..
And
another one .. which includes a piccy of the Concorde slip indicator. Bellerophon was a Concorde pilot in the heady days when the bird ruled the skies.
.. and there are a few more threads around worth a revisit, I'm sure.