So I got the Big Red Error 3048,3 tonight and had to run Remove and Reinstall Norton Security. Once all was said and done and I open Identity Safe, it keeps asking me to create a cloud vault. Well, thankfully thanks to the helpful tips from the 'retaining your local vault' thread https://community.norton.com/en/forums/retaining-your-local-vault, I was able to copy my backed-up copy of the IDStor files into the new version of Norton IdentitySafeDataStore and voila, I have my local vault back.
I'm planning to get a new computer in the next couple of months so I guess this was my pre-test. At least I feel more confident about getting the new computer.
Thank you Norton Community and PRIOR and PhoneMan, in particular.