Bhakti is like loving someone. It is not done for any gain or benefit and advantage we may get but out of the heart’s flow of love towards the Divine. Do we love people because of what we can get from them? Perhaps many do. But true love is not done due to any reason but because of the self-existent nature of love. It is simply for the joy of loving and giving that one loves.
When God is calling away a true bhakta, perhaps to give rest for some time in His lap, the person himself would not feel any disappointment but would rather be happy. Yes, people who are left behind feel sad and may even interpret it as a cruel act. But that is because we see the body as everything and death of the body as the end of a human being. But that is not how God sees us. He sees us as a soul on its eternal journey in which He is the eternal companion and guardian. Bhakti is based on this deeper recognition of the soul that while all other relations are transient and based on the physical nearness, vital interests emotional interchange, intellectual companionship, the relation of the soul with God is permanent and lasts not only beyond one lifetime but runs and grows through all the lives. The soul knows it within even though our mind and outer personality have forgotten it. This knowledge is the basis of true bhakti. All else, that is often given the name of bhakti is largely commerce and bargain rather than the spontaneous flowing of love between the soul and God.
Having said that, there is no evidence that bhaktas have to die early, in fact, the experience of devotees has been otherwise, they always feel around them protection and intervention. Of course I am speaking of genuine devotees who truly love the Lord for the sake of the Lord which has little to do with being religious, visiting temples or doing daily poojas. A person may do all these things regularly and yet true bhakti may be missing. True bhakti is in fact very rare and if one finds it then it is a special Grace. Such a person is always happy with the Lord since in life and in death he is always with Him, which is what the bhakta truly seeks.