A fellow Vienna Instruments user gave me instructions late last night on how to successfully eliminate all traces of the current eLicneser so that the previous version would be able to install. Altogether it took me about three hours to recover from the original problem, but in the end, and after a brief panic when the key showed up with zero licenses (I unplugged it and plugged it back in and did a rescan, which fixed that problem), all of my Vienna Instruments and third-party licenses once again show up on my USB key.
Nevertheless, this incident makes me VERY nervous going forward, and is biasing me against eLicenser. This is not acceptable behaviour for an app whose sole purpose is to prevent software piracy, and which can lose days of productivity for working professionals when something goes wrong due to negligence on the part of the license software vendor (now Steinberg).