There's no way FFXVI hasn't already been worked on for a while. SE always has had several mainline FFs in the pipe at the same time. Hashimoto, or producers/directors in general, always deny the existence of games they haven't yet revealed. Was the same with FFVIIR, see my post above.But not even a small core team working on it? If they really aren't working on FF16 at all, then I guess Tabata was right in that the continued existence of the franchise depends on the success of FF15.
Also regarding FFXV being make-or-break: no, it's not.