Which part are you actually worried about?
You are covered for when you've spent a certain percentage of the "pre-departure costs" on your card. Shouldn't matter that it's on stand-by except that you wouldn't be able to claim travel insurance for the stand-by flight OR accommodation etc related to it.
Eg. Get over there (eg. LA) on stand-by ok, but because you can't get a flight back due to loading, then you're not going to be able to claim for accommodation whilst you wait a week for a flight back!
The most important part of requiring travel insurance these days would have to be for medical and that would not be an issue.