Same style motors and process for determining serviceability as other RC toys. Manually manipulate motor body feeling for end float, axial play and any roughness/binding. You have four so an opportunity to identify any inconsistencies. Also feel after flight for one that may be significantly warmer than others. Fly with confidence.
It's hard to say, depending on the weather conditions, how aggressive you fly, how many times a day, etc.... But I should imagine 2 years if your going out on about 8-10 flights a week but I'm not 100% on that lol