Good bye or bye-bye or bye. 

See you.

So long.

Good night.

See you later.

See you again.

See you around.

Have a good time.

See you next week.

Have a nice weekend.

I’ll see you after class.

Take care and have a nice day. 

Give my best wish to your sister.

So long, Tony. Say hello to your brother for me

I must be going. Thank you so much for a lovely party. 

I have to go now. Call me when you have time. 

Good bye.