Regardless of whether evolution is valid, the fact remains that there is genetic similarity between humans and other animals. It's irrelevant to medicine whether we have an explanation for why this is so. Your hypothetical situation posits not only that evolution be falsified but also that actual observations about genetic similarity among species somehow disappear, which is obviously pure fantasy.
In other words, even if evolution were falsified (which is always a possibility in good science), there would still be genetic similarity between humans and mice, and we could still do medical testing on them to understand ourselves.
Yes, I'm quite aware of this. I'm speaking in hypotheticals and you're speaking in literals.
Evolution is good science and it can be falsified. The reason why it hasn't is because it has overwhelming support in evidence. Evolution though, will never be overturned for a completely different theory. Little changes might be made, but as a theory it describes the nature of how things work too well. The ideas of Common Decent and Natural Selection are far too well supported to ultimately be completely false.
If, for example, we find panda bones from the Paleoarchean, then that throws a big monkey wrench in the idea of Evolution and it might wind up mostly falsified, but it wouldn't be completely falsified, and that's a such remote possibility it's really not worth bothering with.
So I was hypothesizing, "what would a world without Evolution, Common Decent, and Natural Selection look like?"
Your point remains that mice and humans are
genetically similar. However, my point is they are
genetically similar because they have a Common Decent. And the ways they are dissimilar are because of Natural Selection and Genetic Drift.
However, if evolution were found to be completely false somehow, you are correct that the observations wouldn't change, and that reality would be that mice and humans are still somehow genetically similar.
So to sum up, you're right, and I'm right, but we were talking about different things.
"well then where did the first organism come from?".
That's Abiogenesis, not Evolution. It's offtopic.