Witnessing an animal's death

I have seen dead animals, but I have never seen an animal die in front of me. Seeing a dead animal is very sad on its own, I can't imagine how hard it is seeing an animal die before your eyes, especially a beloved pet. I have heard a lot of sad experiences from other people, similar to the ones posted here. The saddest ones are where the animal somehow survives, and you know there is no way to help her I really don't know what I would do in that situation. I hate to think about my cats deaths, but when it does happen I hope it will be of a natural cause, and that I will be beside them when it happens, offering them some kind of a last moment comfort.