You can't say never. It's possible that Vancouver could get an NBA franchise again, but it's not on the NBA's to do list, that's for sure. There are still some big markets that don't have teams. From what I've read about expansion or moving teams, Vegas is one of the top options for the league to get in. They're not going to choose Vancouver, a market which has already failed once, before they choose a city like Las Vegas.
You can't say that it will never happen. It's probably safe to say that the Raptors will win a championship or two before Vancouver is even mentioned in expansion talks.