OneKartVita on 01 March 2016
It's almost dead in the US. Europe will keep buying it for a few years as long as the strong Japanese support continues.
Japan at a minimum 2018 but I can honestly see it going even longer. They already have great Japanese support but if the NX handheld is similar in power the vita might actually start getting more games.
Either way the answer is, when the Japanese stop buying it which will be a long time.
