I was able to get MureDenoise and MureDenoiseDetectorSettings back by reinstalling PixInsight from the latest download. After doing this, I could see that the Mure Denoise scripts were back in the src/scripts/mschuster directory. But I was still missing the Script -> Noise Reduction menu in PixInsight.
I allowed an update to run, but no change to the script menu.
I next opened Script -> Feature Scripts and then re-added both versions of Mure Denoise using the "Add" button and navigating to the folder for each script inside PixInsight.
I am not sure what happened. Perhaps this is a glitch that only I experienced.
I hope this helps someone else.
Andrew