Tricky one this. The non run flat tyres would still be fit for purpose, but having said that, if you get a blow out with them on, then maybe the accident could have been prevented.

At the end of the day its a saftey feature to prevent accidents or loss of control at least. But is it actually 'classed' as a safety feature or a convenience type-thing to get you home when you get a puncture?

Ive known insurance companies to void payouts for injury claims if the airbags been removed, which is a saftey feature. Would they pay out if the ABS was not working and you locked up and hit someone?

Same principles really.

Edit: check the owners handbook and see if it says 'we reccommend that you replace tyres with run-flats' or anything like that. Look for the words 'reccommend' or 'must'.