If Satoshi should appear all of a sudden, it already partially means good-bye to our dear decentralisation like I explained before, since the government can now have a central body to indirectly control the network.
Secondly there would be an unfriendly shift in bitcoin price and also a general dip in the crypto space since the government would want to take control of the coins he mined ( picture the effect of moving about a million coins on the network)
The bitcoin network would likely experience some changes that may not support discentralization coupled with the fact that Satoshi's appearance may cause vulnerabiliies to appear in bitcoin's protocol.
The things mentioned by you seem more like BS to me.
1.Satoshi Nakamoto doesn't have absolute control over the Bitcoin blockchain.
2.Why would the government(I guess that you refer to the US government) want to seize the 1 million BTC in Satoshi's wallet?
Did Satoshi do anything illegal? I don't remember governments in democratic countries stealing assets from their citizens just because they want to.
3.The potential crash of the Bitcoin price also makes the idea of government confiscation kinda pointless.
4.If the Bitcoin protocol gets changed and Bitcoin becomes more centralized, many Bitcoiners will sell their BTC and leave the community, which also makes the whole idea counterproductive and pointless.