In khula, will the wife have to pay the full mahr?

If it was paid up front and then some deferred amounts paid, then she would pay what was paid up to that time.

Or could simply negotiate the amount that she would pay. Say, look, I'll give you whatever you paid me up front, nothing more, nothing less. That would be acceptable as well. So generally scholars are acceptable that the mahr whole or in part can be paid. There is a difference as to whether more than the mahr can be paid.

I believe the majority of scholars do not allow that.