A back of the envelope forecast for "long-COVID" impact on IP claims:
Start with cases - about 1,950 if we are considering current known cases, or whatever number your modelling predicts for whole of pandemic. Assuming very good containment, not much more, let's hope it stays that way. The apply your estimate for "long-COVID" I am using 20% at the moment which gives us about 400 cases in New Zealand. But not all of these will be in employment and own income protection. In fact as 42% of cases are 'imported' we can assume that most of those do not own income cover issued by New Zealand insurers. That leaves us with roughly 240 cases. FSC underinsurance research showed income protection cover at about 20% of the market - or a possible 48 cases of 'long-COVID' where a claim may be possible.
Well, well, within the capability of the industry to manage. Economic impacts on people that have claims from other causes are likely to be more problematic.