IF you die before selling the data, you lose the exploration data for that system and you do need to FSS the system again.
Yes - except that any inhabited system will either be on the "shared exploration data" register or high-population enough to start out auto-discovered.
You might lose information about what the planets
are but you should still be able to see them on the map and radar just as you would if you jumped into a new-to-you previously explored system.
And it seems to only be a case of "a few planets in the system goes missing" rather than the entire system data: the gap is visible and obvious on the map from the planets you can see - sure, it's
possible that someone scanned all but one planet, sold that data, came back to scan the remaining one, forgot they hadn't sold that, died, and then it was missing when they came back again ... but it seems to come up a lot for such a convoluted sequence of events.
It's obviously not going to be fixed - it's not a bug in the Frontier Issue Tracker sense, and if any veteran players were going to spend time turning it into one they'd have done so by now - so workarounds are all that can be advised, of course.
