In my view, resistor failure is most unlikely. The resistor will even withstand kV surges, which can't be assumed for the capacitor and for the amplifier still less. You can measure the resistor by applying a voltage and measure the current with a usual digital multimeter in voltage range. E.g. 200 mV range, 10 MOhm input resistance has at least 0.1 nA resolution.
Knowing the appliclation, it seems almost ridiculous to consider a self-elaborated resistor, I think.