(I am writing this from the American perspective.).
I was just in French Polynesia and they have a set procedure if you test positive upon arrival, but there wasn't a clear procedure for "what if americans test postiive before return?" While we were there we spoke to the US Consul who said he was currently dealing with 20 positive american cases and was trying to find them local accomodations.
We do know of someone who tested postiive before return and was able to arrange to stay in their resort bungalow for 10 days until they got a letter stating they were negative and able to fly again.