gunmetalgator
asked:
What changes from a pony being transformed into a changeling drone in terms of their behavior and actions? What happens to the drones' previous lives; do they return sometimes to not have any suspicion of them turned into drones or are they simply missing from pony society?

It depends on the Queen.  A drone maintains the vast majority of their own mind and will, and the only real change is the introduction of new instincts and an intrinsic loyalty to their new Queen.  Some Queens will have their drones make appearances to avoid suspicion, where others will stage things to make it look like the pony has vanished, or the pony just vanishes. 

Papi will have to learn soon how important maintaining secrecy is.