This is my concern too. I've had mine for a looong time, but not their entire life. When I adopted them they were in a bad state. It took a lot of love and trust to build them back up and there is something undeniably unique about our bond. I hope I go before they do, but that's unlikely. In the likely scenario that they go first, I can't imagine having that same bond with another pet. I obviously would prefer no animal has to experience what they went through, but there is just no way our bond will be as deep.
I feel a little messed up saying that because obviously every relationship is different, and I'm sure most furry friends are capable of deep love, but I will never be able to demonstrate my love the same way to an animal that doesn't need that help. If they never needed to be carried, how will they know I will be there when they do? My little one knows I will care for them through anything and I just want them all to know that without having to have experienced the need for it.