I run mine year round, the climate is never off. Only time the aircon compressor doesn't run is when its too cold.
You don't have to go back to Seat but I would expect if you were to have any issues with the aircon and it hadn't been serviced on schedule they might refuse a warranty claim. No warranty probably no point.
My car will be serviced now on outside of the Seat dealer network but by specialists as the warranty ran out last month.