Their published warranty period is 90 days as follows:
"Warranty
All of our exhaust systems are warranted against defects in material and/or workmanship for a period of 90 days. This does not cover finishes such as plating, or painted surfaces with discoloration or rust. This warranty shall be limited to the repair or replacement of the system, which may be proven defective under normal use. We will not warranty any system that has been abused, misused, improperly installed, or modified.
Dealers or distributors are not authorized to make dispositions binding upon Vance & Hines. We will not be responsible for any labor charges incurred in removing or replacing any system under warranty. All returns must be accompanied by a return authorization number and a copy of the purchase invoice. Parts being returned without a return authorization may be refused at our receiving docks."
There is nothing specific to the FP3.
It does NOT have to remain plugged in after flashing the ECM unless the rider wants to be able to use the "View Sensor Data" feature of the unit. Also, if the rider wants to use the AutoTune feature, the unit would need to be plugged in for a short period of time while the unit builds the map.
Cheers,
TQ