Such an interesting discussion here.
I think we can see a real life example of this happening - when the students do not practice the teachings or have gone against the teacher's wishes or instructions, the teacher's great work cannot manifest.
Hence, if the teacher's great work cannot manifest, the teacher will not see any point in staying.
More than going away, the teacher may even leave and disrobe.
Case in point, Lama Yeshe's current incarnation, Lama Osel.
It is beyond sad. It is a tragedy!
A teacher's great compassionate work will benefit so so many beings. Hundreds and possibly even thousands. Not just this lifetime, but even consider how much Dharma seeds he or she could have planted as well.
Without the teacher, no student can come into his or her full potential.
Not only does our path to Enlightenment ends, we have also destroyed the precious chance for others to gain any sort of Enlightenment and Dharma.
That is a HUGE LOSS.
Immeasurable.