Age would certainly be a factor. If I lost Merlin NOW let's say (at 4 months) searched high and low.. and then 2 years later found him with another family, grown up, happy and loved.. I would probably let him stay. At that point, he would've been theirs longer than he was mine, they RAISED him, they KNOW him as the adult dog that he is, I knew him as just a baby. I would of course put them in contact with his breeder. BUT Merlin is a puppy. A young one at that. I love him dearly, but accept that if he was lost and then found by another family, raised, and grew up there.. that frankly, they would have more of an attachment than I would...they would've raised him. If Merlin was lost as an adult, that's a different question all together. For me the bonded thing isn't much of a factor. the dog is more used to them, and if they were lost by way of natural disaster, there is also an issue of you being associated with scary things. To me, a dog appearing more "bonded" to one person over another isn't necessarily indicative of love for that person...this dog has likely been fed, watered, loved by these people over time, of course there is an immediate knee jerk bond to what is more immediately familiar. I of COURSE would expect a period of adjustment (whining, dog being upset, out of sorts etc.. at being brought home), especially if the search for the dog was very long (6 months +), I don't see this as more LOVE for the other family/loving me less but moreso just the animal trying to adapt the change. Honestly, if anything, the families reaction to losing this dog would be more likely to sway me than the dogs reaction. The age/time they spent with these people/their reaction to losing this dog would be more of an issue to me than anything else. As well as of course condition/care of the dog. And I don't mean "care" like "Oh they feed raw" I mean..is this dog part of the family? or "just a dog" to them?