If Satoshi would reappear, I think he will most likely refuse to take the role of leader, because he wanted Bitcoin to be developed by open source contributors, with approval from the community, which is what we actually have now. It might even be one of the reasons why he choose to leave, so Bitcoin won't have a weak central point, like for example Vitalik Buterin is for Ethereum's network - just remember how the price crashed some time ago when someone started spreading rumors that he died in a car accident. So, from a technical standpoint it doesn't matter who is Satoshi, and if the market is rational, it shouldn't strongly affect the price.
If he did come out of hiding I feel like the markets would react very harshly. Not necessarily because he appeared and because it might have some sort of impact (he probably would not have a significant impact anyway-- Bitcoin has been doing fine without him), but specifically because of the market trying to overpredict itself. It would be just day traders trying to out-trade themselves. I would honestly be surprised if a significant price change caused by this were to last for the long term, whether it be an upwards change or a downwards one.
