I should elaborate. The information on Yokuda is almost nonexistant and the Redguards have lived (supposedly) exclusively in Tamriel for a long time now. It is never explained HOW it was destroyed or what exactly it being destroyed entails, so it could still have people living there even. I have not seen any actual source saying it was 'sunken', simply 'gone' or 'destroyed', which is very ambiguous. I don't even understand how a continent that big COULD 'sink'. Also, this is 200 years later. Lots can happen.
I believe it was sunken by earth quakes, although Redguards seem to believe it was a result of something of their doing. I guess it could pop up again, but I don't think so because that already happened to Thras with the Sloads. But really, who doesn't want an Atlantis-style under water city populated by mer-people.?