This depends entirely on imprint templates, imprinted features, inking methods and chemistry used.
We experience with imprint templates used in our machines that have done thousands of imprints. Verification has been done by optical methods, measuring the diffraction efficiency of holographic features (which would correlate with changing dimensions of the nanostructures). No SEM data are available at this time.
In our experience, degradation is due to buildup on the imprint templates.