"Thank you and goodbye."
Translation:Tak og farvel.
No, it should not. "Takker" is often used in a very informal way.
Unless you are saying "Jeg takker jer" ("I thank you") when speaking in front of a crowd, don't use "takker" unless you're talking to friends.
An example where you can use "takker":
Jeg takker jer alle for at komme her i dag = I thank you all for coming here today.