I'd probably be happy and shocked at the same time.But if all the animals in the world were replaced by pokemon over one night most people would freak out saying it an alien conspiracy or a military experiment gone wrong.The world would drastically change and no one would trust anyone anymore and amongst the chaos I would rise to be a pokemon master and save the world.
But in all seriousness everybody aren't pokemon lovers like us so i think there'll definitely be a bad outcome if it happen, probably people taking advantage of the unnatural powers pokemon have.
I said slowly and gradually, not over night. That would be outrageous. But yea a bunch of good and bad could happen from pekemon becoming real. I myself would almost explode from excitement/shock at first. But to tell you to truth other than that, given the speculated circumstances, I cant tell you exactly how I would react other than that.