Not lose control exactly. But if ICANN is willing to, they have the power to simply make that control irrelevant in any specific case. The government in question would have absolute control of a TLD registry that no one else considers authoritative for that TLD. If you're a hermit kingdom like North Korea anyway, that's probably not a big deal, but for anybody else it's liable to be a very big deal indeed.

I would expect ICANN to use that power very sparingly, preferring to publicize rather than act as a first step, and if they did get heavy-handed, again they would incur a hit to their legitimacy.

The only reason it's considered unthinkable that could happen to .com is that everybody agrees it's unthinkable to do that to .com. But ICANN absolutely could make a credible threat to US control of .com or .us if they felt it warranted to do so. (You could say they're ICANN, not ICANN'T.) They could do the same to .gov, for that matter, but the US government already explicitly owns and controls that whole hierarchy, so there's no real "interference" issue there.

The whole Internet's viability is based to some extent on the collective delusion that everybody agreeing this is how it works, actually makes it how it works. But none of that is set in stone... which is generally a good thing.