Utterly tragic. An accident like that could happen to any single seater driver at any time - it's one of the risks you take in an open cockpit car. In Jackie Stewart's autobiography, he described how, back in the 60s and 70s, all the drivers started the race wondering if they were going to finish it, and who wasn't going to see the end. Regardless of the risks, motor racing is, and always will be, a very dangerous sport, and you can never eliminate all the risks; an accident like this could always happen with open wheel, open cockpit cars. Everyone seemed to have forgotton that - all drivers know it could happen, but probably not to me - and Henry's accident is a timely reminder that it can happen, does happen, and will always be a possibility with this sort of car.
Good luck and best wishes to Jack Clarke - to know your (or possibly someone else's) mistake has killed another driver must be a terrible burden to bear.
None of which makes Henry's passing any less sad. RIP Henry, you died doing something you loved.