TRP seems to think no one will ride their rotors enough to need to replace them....none of their documentation states a wear-limit, as far as I can tell. Ask them. They aren't alone,
I remember reading a Zinn column where even he couldn't find SRAM/Avid documentation on wear-limit for those rotors.
Generally wear limits vary from 1.4mm (Hope) to 1.8mm (Some Magura) depending on the OEM. Generally....the wear limit is a loss of 0.2mm (Hayes, Magura, Hope) to 0.3mm (Shimano) from as-new thickness.