We can, however, make some assessment of the probability of it existing.
If you truly follow the argument that you and others are making, you cannot say that anything is unlikely to exist unless you can absolutely prove its non-existence...and how would you do so for anything? For anything that is untestable, you must either think that there is an equal chance of its existence and its non-existence or completely dismiss any consideration about the question of its existence.
Even something I make up right now, e.g. that the supreme creator of all things and the One True God of humanity is called Bing! (note the exclamation mark - it's very important), is a 17-legged spider and currently lives on top of the door frame of my bedroom. Not that you could see Bing! even if you were here, or detect Bing! using any equipment or the senses of any animal.
You cannot prove any of those statements false, therefore you have to think of them in exactly the same way as you think of Christianity and every other religion that exists, existed in the past or will exist in the future. As well as the undetectable mastadon that lives underneath my kitchen sink, of course.