if you do this will the ECU loose its memory and would require you to start all over again with reflashing the ECU with the AP? or would it hold the tune in its memory?

It will keep your basemap on your ecu, but your realtime map will be lost. Also the ecu will forget what it has learned since the last time you have done a reset (ex. IAM will be reset to 12)

the only "memory" that is lost is what is stored in the ecu that "learns" how you drive your car. it makes minor timing adjustments based on driving conditions. so if you drive like a madman the timing may increase a little, but if you're in traffic a lot, it may pull back the timing...