This is a fun thought! I think it’s pretty much universally accepted by us the writers that once one leaves the Lounge, they carry on in their usual AU like they never left, not remembering their time mingling with the other AUs.
That being said, Sherlock would certainly want to do as much science as he can before he leaves the Lounge, as long as he’s allowed the proper equipment. Testing blood samples, comparing and contrasting reactions. I can see him snagging a hair from giant!Jacob to examine closely at such a large scale. Anyone who messes with his science will be scolded! …unless they’re a smol kiddo, in which case he will have absolutely no evens.
If he could think of a way, Sherlock would most definitely try to sneak into other AUs, if only to see how the main characters of that world interact with it and deal with their cases and problems. Whether or not he’d succeed is a different story.
Brothers Apart 