Always amazing to find we haven't solved it yet! So some more crazy theories - first, if we do let one expire, just in case it is warping away, perhaps we should do it in a system that only has one possible jump out of it. Of course we have no idea what the jump range of a UA would be, if it is jumping, but it might give it just one place to go. Could have someone in the other system, though the odds of spotting it before it expired again would be low. Just a thought, if we are going to do it, may as well do it like this?
Next up - Voyagers disappear, Leonard Nimoy station, well, if we skip the whales, the first Star Trek saw a Voyager picked up by aliens and made sentient. Perhaps the UAs are Voyager, or some probes from a greatly enhanced Voyager? I do believe whale song was included on the Voyager golden record? Not sure what would come from that, if it were true, then what? Where we go and what we do with the UA, how would we find the modified Voyager etc. But again, just a thought.