If you have travel insurance for a trip to France in November (with cover running from November 7 to November 22), and the people who rent out the apartment go bust in, say, September, does the policy cover you?
It depends on whether the policy covers you at all for this sort of thing - many or even most don't.
If it does, the date they go bankrupt does not matter, you should be covered.
If you paid by credit card then that may cover you.
Normally you are covered from the date on which you take out the insurance for things which could go wrong before you travel, eg illness etc.
However, without seeing the wording of your insurance it is not possible to see if you are covered. Also you might be covered if they are bonded to an organisation such as ATOL or if you booked through a travel agent.