Life in prison. If it risks the lives and sometimes costs the lives of Americans performing a highly dangerous mission for America, I support life in prison even if the name of just 1 informant is given
Granted it probably risked the lives of non-Americans even more performing a dangerous mission for America. American agents are usually not harmed, it would be a major fuck up from the Chinese side to knowingly assassinating CIA agents. But what they would not think twice about executing Chinese agents who supplied information to the Americans.
https://www.law.cornell.edu/uscode/text/18/2381 Whoever, owing allegiance to the United States, levies war against them or adheres to their enemies, giving them aid and comfort within the United States or elsewhere, is guilty of treason and shall suffer death, or shall be imprisoned not less than five years and fined...