In a common exchange, one might give one answer, and then change their response on new information.
A: Want to see movie X tonight?
A: It starts at 11pm.
B: Then no.
Is the above usage of "Then no" proper or should it instead be "Than no"? Obviously, there are other grammatical usages possible, but this question is specifically asking whether "than" or "then" is proper in an exchange like the above.