Take two: Slàn leat!
An dàrna turas: Slàn leat
Look at the conversation again:

Ciamar a tha thu?
How are you?

Chan eil gu dona. Tapadh leibh. Ciamar a tha sibh fhèin?
Not bad. Thank you. How are you, yourself?

Mise? Tha gu math. Tapadh leat.
Me? Well. Thank you

Slàn leibh!
Goodbye!

Mar sin leat!
Goodbye!