Expat (i.e. US citizen living outside the US) gets to vote in US presidential elections, even if no residence is retained in US (and therefore has no basis for voting in local elections or elections that select regional representatives, including Congressional reps and senators).

There is some question as to how well those ballots are counted, but that's another story.

But citizen privileges and responsibilities, including filing for taxes, are retained.

By the way, lots of municipalities in US have similar tax rules. In New York City, when I lived and worked there from the 1970s into the early 1990s, if you maintained an unincorporated business you had to register with the city and file even if your earnings were below the threshold that triggered tax payments. And the penalties for nonfiling, which were substantial, applied regardless of how much you earned or owed. Much the same where I am currently in Virginia.