No one claims that genes will live forever and even beyond the heat death of the universe. The term "immortal" in this context means that it lives far longer t

No one claims that genes will live forever and even beyond the heat death of the universe. The term "immortal" in this context means that it lives far longer than individual organisms. A gene will typically remain unchanged for many, many generations of ephemeral individuals. We can talk about "a gene" while talking about the same thing in multiple individuals in the same generation and in multiple generations. It's a piece of binary information. Of course, eventually, a gene may vanish because no individuals survive that carry it (e.g. due to competition from other genes, or because the entire species vanishes in some catastrophe).