A brake-pad inspection is a useful opportunity to check rotor thickness too. Start by identifying the rotor model and its wear limit: a figure from another manufacturer does not automatically apply to your disc.
For SRAM’s 1.85mm rotors, the minimum is 1.55mm; for its 2.00mm rotors, including HS2, it is 1.70mm. Replace a rotor below the applicable limit. The Maven pad separator also has measuring slots: a rotor that fits into its designated slot needs replacement.
Shimano hydraulic disc-brake manual UM-0RM0B specifies that a rotor must not be used at 1.50mm or less. Cracks, deformation or an exposed aluminium layer on the braking surface also rule out continued use.
Let the brakes cool before inspection. If you cannot establish thickness confidently, have a bicycle workshop measure it. After replacing a rotor, follow the bedding-in procedure for your brake system so the pads and disc can develop their intended braking performance.