Hi weaver
I think your overthinking this sorry
Moving a connection from port x to port y on a smart switch, the switch table already knows the MAC of the device, and say your device been sent to does not change port, then it also knows this, so directs accordingly
I'm not sure I understand you data in flight, but if any data is in transmission when you unplug the losing device your removing, this data would be lost, due to no route, but it minuscule as your only talking of the data last sent by the losing device been removed. Simply turn the device off before unplugging from smart switch
On roaming, this is for waps and not your smart switch to do, and should follow as above on port switch detail
As I said, I think your overthinking this sorry, but apologies if I am wrong in any way/description
Many thanks
John