We don't know what happens, Sherlock (in my opinion), had it all planned out to jump off that roof and I don't believe his smack on the pavement happened oh so as it seemed.

Sherlock is too smart to jump off just because Moriarty said so (he doesn't exactly like doing what others tell him) and he did ask Molly for her help (possibly to presume him as dead and give everyone who knew him a fake corpse).  I think Moriarty also had something up his sleeve because no matter what information he would have wanted from Moriarty he wouldn't have sold out his brother's life story.  The only way he would have is if it was all to set him up at the end.

Then again just my theory guess we will all have to wait for sure until the next series.

BUUUUT....if he did have Amnesia I think he would act the same with everyone.  No matter if you can't remember others you cannot change who you are.  I think everyone would take it hard.  John would probably get him back into the swing of things with Lestrade and just keep blogging.  Molly, well she always like him she may see it as another chance to win Sherlock's heart, but not try to take advantage of the situation.  Mycroft is his brother, so he may try to get sherlock back for somethings (harmless paybacks), but probably do everything he could to make his brother well again.