Fyrwald has been appointed because he is American, in the hope that this will help convince the CFIUS / USDA / FDA that new Syngenta will be the same as old Syngenta. That's an ambitious hope, because Syngenta will undoubtedly change dramatically, and quickly. The focus will be on bringing existing corn and soy technology to China, on running the business for cash elsewhere, and on migrating manufacturing and other activities to China. There won't be much cash in the new Syngenta for new product/trait development, or any other investment. The US business will undoubtedly decline, and for every dollar lost in the US/Canada, they will need to make an additional three dollars in China to even match existing profitability.
This is assuming that the Chemchina deal actually goes through, of course! There's an increasing school of thought that this may not happen, and that Syngenta has gone through an elaborate facade in order to buy time. Why on earth would you want to carry such a large amount of debt, and suffocate the business as a consequence? Now its competitors are doing less well in difficult markets, and there may soon be the prospect of an industry merger, on Syngenta's terms.