[Note: this is purely hypothetical]
You have agreed to feeding a friend’s beloved cats while they are out of town for a couple of weeks on an expensive and much-anticipated trip. The animals all appear to be healthy when you take over for their care. Three days after your friend departs, through absolutely no fault of anybody, one of the animals suddenly dies; it can neither be foreseen or prevented in any way.
Do you contact and tell your friend immediately, certainly ruining their trip, or do you wait until they return?