Full blood Zetas will continue in other parts of the Universe. Some of our Zetas reflect their genetics unaltered except as evolution has affected them. They reside on planets that for one reason or another did not conduct genetic engineering - they did not know how, chose not to, or were failures at it. Your human culture, for instance, is only in the preliminary stages of understanding the human genome. But even if you were to grasp the concepts, your culture has great resistance to being engineered, in great part because of the strong Service-to-Self elements in your culture who would distort the purpose of such a program. Due to the wide variety of Zeta types, there are no characteristics that could be called out to distinguish the unaltered Zeta. There are several such Zeta types, all more dissimilar from each other than they are from altered Zetas types.
Some entities have indicated a desire to remain in their home galaxy, in existing Service-to-Other communities, and this desire has been granted. They will continue as is. Other Zetas have migrated to other planets and galaxies, for one reason or another, and will continue to reproduce themselves there, as need be for continuance. The full-blood Zetas on Earth expect to migrate into hybrids, along with humans. We have a vested interest in having the hybrids be as delightful an experience as possible. The Zeta have not, in their past genetic engineering, merged with another hominoid race. This is one reason our learning curve has been so steep, this past half century, while developing a Zeta/human hybrid. As these hybrids carry many distinctly human traits, they are never confused with the other Zeta types.
One should also not assume that full-blood humans will die out entirely either. This almost never occurs during species transitions, especially when a certain level of intellect is attained. There may be Service- to-Other groups on Earth composed entirely of humans that continue, isolated, and content with their level of intellect, for instance. There will be Service-to-Self entities, taken before their human form is terminated, who will be human on other planets. This occurs frequently in the Service-to-Self orientation, as surviving infants are hard to come by in this orientation. Nurturing is rare. Thus, those choosing this orientation often are required to keep their current incarnation.