I don't think Satoshi's reappearance would be a bad thing per se.
Some want Satoshi's identity confirmation and reappearance but others don't want it.
I agree that it's better the way it currently is, but it would not be the end of decentralization, as Bitcoin is designed in a decentralized way.
It's biggest strength of Bitcoin that makes Bitcoin is unique while in cryptocurrency industry and market, there are thousands of cryptocurrencies but none of them can replace Bitcoin, because they are centralized.
Also, it might draw a lot of attention to Bitcoin and excitement that Satoshi is back, which might actually be good for the price (depending on whom the person turns out to be).
I really don't know. It can create both, fear and excitement and because it hasn't happened, we can not know its effects that can be negative or positive on Bitcoin price.
I don't think any government would have any claim to Satoshi's coins, similarly to them not having claims to anyone else's coins. What they can get very interested in, however, might be taxes, depending on Satoshi's tax residence.
Taxing residents is target of governments and they are good with taxation citizens. Recently in Italy, government made a proposal of taxing 40% of Bitcoin profit because they think it is too easy to get profit with Bitcoin.
Italy Reveals 62% Increase in Bitcoin Capital Gains Tax. They want to increase tax rate from 26% to 42%, that is 62% increase.