RF load (terminator) at the end of RF attenuator
If your attenuator is beefy enough, you should be fine without a terminator.  If a signal does bounce off and come back, it will be attenuated by 2x the value of the attenuator since it passes through the attenuator twice.  Say, if you have a 50 dB attenuator, a signal that passes through the attenuator and reflects back should be attenuated by 100 dB.  So some will reflect, it's just a question of whether it is small enough to cause a problem or not.  100 dB return loss is pretty darn good even for a terminator.  The return loss of a loose connector is probably worse than that.