The answer to this is in your insurance policy, not the Act. If it’s a like for like, insurance, then you are covered. If it’s based on the valuation, then you may have to consider things like CPI but I don’t think that’s as relevant as having an effectively vacant site (in the event of a catastrophe) available to developers.
Policies differ. Our building is insured for a rebuild … but not necessarily on the current site. And bear in mind that while material and labour costs will rise, building techniques are constantly improving and you could conceivably end up with a better replacement building that cost less that the original.
But your first port of call should be the insurer who will explain exactly what you are being insured for.