How do people in Bangladesh say goodbye?

people of Bangladesh don't say goodbye as it is in English, these are same of the word which might help you.

Abar deka hoby (see you again)

Ekon Ashy (I will leave now)

bhalo teko (be safe)

Salamualikum. (peace be upon you, If you are addressing to muslim)

Adab (respect If you are addressing to hindu or buddist)

I hope this will be helpfull to you.