Apart from cells, what are you referring to here? Especially, is there anything that can be considered "somewhat living" that is not a by-product of regular life, which as far as we know has only ever appeared (or thrived) once Earth's history?
We know of no other planet that has waterfalls.
Yet, because we have seen enough waterfalls on Earth we have an evidence-based scientific belief that waterfalls cannot be Earth-specific because all that is required for one: water, erosion, gravity -- exists throughout the cosmos in very large amounts.
Life is the same. We have seen enough of it in enough variety to know that it can take on many forms, including exotic forms that are impossible on Earth but would be possible elsewhere. The abundance of the ingredients and time are all that's required.
Furthermore, unlike waterfalls, we actually have no idea how life appeared and, despite trying for many years, have been entirely unable to produce life from non-living things, and we have never observed this process occurring naturally either.
Furthermore, every living thing we've ever looked at has been a relative of other living things - as far as we've been able to determine, all of the life on Earth has a single origin, a single original RNA/DNA code which must have been present in a single population of organisms, at a single location. This is a strong suggestion that the conditions that allowed life to appear on Earth may have been extraordinarily specific - otherwise, we would expect many unrelated beings sharing the planet (or at least it means that a particular for of life was overwhelmingly more adaptive and entirely wiped out all of the others).
Even worse, there is another phenomenon for which we only have evidence of one instance happening in the history of the Earth: all eukaryotic life has a single common ancestor, and there are no complex multicellular organisms which are not eukaryotes.
So, not only did life arise only once on the one planet we know it can thrive in, but complex life only arose once from simpler life.
So, while we can't say that it's plausible life will never again arise in the universe, we can say that for any particular moment of time, it is plausible that no new life is being formed anywhere else in the universe.
As far as we know all life is related and has the same ancestor. Even on earth the emergence of life seems to be a freak accident.
However, for structures where we have no idea of the process by which they are formed (like cells), we can't have any opinion on how likely they are to happen elsewhere, unless we see more examples.
What forms of life that are impossible on earth do we know about?