Let's say that a student told his Yeshiva that he will be returning the following year. For whatever reason, the student changed his mind.
At what point must the student tell the Yeshiva of his change of plans? Must he tell them immediately, or can he push it off a bit, and tell the Yeshiva closer to the start of the year?1
On the one hand, it doesn't matter to the Yeshiva whether the student comes or not; they will be giving that class anyway, regardless of one more or one less student.2 On the other hand, perhaps, since the Yeshiva is assuming that the student will be coming back, if the student doesn't tell the Yeshiva otherwise, it would be misleading the Yeshiva and therefore a prohibition of Geneivas Da'as.3
In principle, this is the opposite of this question regarding a school telling the students that the school is closing. However, the two sides of the question are very different in this case.
1 Obviously I am assuming that there are no previously signed agreements, no Dina D'malchusa applications, etc. - just the simple question of what does halacha say in a general case.
2 Obviously this side of the question would not apply if there really is a difference if that one student comes or not; say, they rely on his tuition to keep their doors open, or if he has a private tutor at the school who will need to be told not to prepare for him. I'm sure you can come up with loads of cases where that side would not apply and therefore every day they assume he's coming costs them. Obviously my question does not apply in such cases.
3 I'm unclear if intentional lack of action that leads to a party being mislead qualifies as Geneivas Da'as. A source proving that this indeed is not Geneivas Da'as would count as a valid answer to this question.