You do lose your licence after a seizure, whether you were driving at the time or not - you can get it back though if you have been free of seizures for 12 months (in most cases, might be longer though depends on what sort of seizures and medication etc).
If we banned people permanently from driving after 1 incident of something that may never happen again... half the country would not drive. It just isn't practical.
Theres lots of ways in which you could end up killing someone with your car and its not your fault - a friend of mine hit someone one night as she ran out into the road straight from the pub where she'd been drinking all day. He was doing under the speed limit, the whole thing caught on CCTV and his dash cam. Should he be banned? It would have lost him his job too, and he'd have had to move house as his home is very rural.
It just isn't practical - if someone commits murder, does their time and gets out, do we prevent them driving? Or is this just for those who cause death with their cars? Or only those whose fault it actually was (in which case why bring it up, as it has been determined these childrens tragic deaths was NOT the drivers fault)...
Again people seem to want not just punishment.. but revenge. Thats not how our justice system works nor is it how any justice system should work!