You said: "One can readily grasp this matter of life melting back into the cosmos if he studies the sutra and cherishes the essence of Buddhism in his heart. "
That suggests at least to me that your identity disappears as well. Yet what I read in the Tibetian Book of the Dead completely contradicts that. The book is very explicit on your continued consciousness from death to rebirth or salvation. You continue to sleep at night if you choose the soft lights during the day, but wake up each day to experience the next set of colored lights and eventually the atmosphere becomes stormy and you seek refuge in a cave that becomes your next birth canal.
So your brand of Buddhism, which seems to be Japanese, correct me if I am wrong, is very different from the Tibetian variety, which is much closer, at least geographically, to the source of Buddhism.
True "Shakyamuni categorically denies the existence of the soul in his Nirvana Sutra, defining this belief as non-Buddhist and incorrect", but you have just replaced that word with the word life. It just seems like semantics.
Since you say: "so too are we born carrying with us undiminished our karma created in prior existences, " when we melt into the cosmos, we do not lose out identity.
So the question remains, what in the melted version of us is preserved to maintain our identity. "Life" is much too general a term to be used in this context. Most non-Buddhists would call the preserved unit the soul. Shakyamuni rejects that word. But not the concept of identity preservation, otherwise karma would not be passed on. This is logical, I think.
Perhaps the word Karma would suffice. What is preserved is not your consciousness but only your Karma in the broadest sense. However, this is still contrary to the Tibetian Buddhist view that consciusness is continuous from death to rebirth.
Can you resolve the contradiction between what you say and what Tibetian Buddhists believe?