Private insurance issue

Complex question. If I were him I would wait and see what happens. An insurance company maybe possible might have grounds for asking for reimbursement of money paid out - but not to fine or punish anyone for something caused by mistake or oversight rather than deliberate fraud. In the end, they would likely have to determine if the condition would have been serious enough to not accept them. If not, then it probably makes little difference. If something in addition needs to be paid, I would think it would mean higher premiums, paid retroactively – rather than paying back the cost of treatment for the unmentioned condition. In the end, the only one who can give a definite answer will be the insurance company.