An insurance company cannot change your coverage limits without your OK or your request, unless they simply drop you, period. And, unless there is evidence of fraud of another type (say, if you are caught lying on a questionnaire), they can't go back and drop you retroactively either.

So, if you have $500 deductible on your comprehensive (which covers auto fires) and your car burns up on a certain date, unless it can be shown that there was some kind of fraud involved, the company owes you a check for whatever the Blue Book (or equivalent) value of the car is, minus $500....a severely burned car, of course, is usually totalled. They can't go back and say "We dropped you two days before it happened". If they do, they will probably lose in court....you'd have a good case.