After this interview, fairly certain he'll stay, but Ogier is most likely to leave. To me it sounds like M-Sport is unable to get the financial backing that Ogier is looking for, but they are however able to get enough that would keep Tänak happy. As he said himself, the car is developed around him and if he was no.1 in M-Sport, surely most of their manpower and WRC development budget would go to helping him. No need to waste time on getting to know the new car but build upon what has proven to work. This is the safest and smartest choice, should he be interested in challenging for the champs title next year, which he obviously is.

Alternative is that he is going to Toyota and what he answered to the interviewer was just the second part of the question:

Q: "So you`d be more than happy to stay where you are and fight for the world championship next year and hopefully be the world champion then?"
A:"That`s the plan you know, i`ve always been the kind of guy who wants to fight [...]"