[Please, don't make this into a political discussion.] Curious - hypothetical person living in the US for years. Decides to go back to home country. Person has valid travel docs, but not entitled to be in the US at this point. By air - issues? Valid travel docs provided to airline, and no formal "exit" procedure, but will airline be looking for return portion of I-94? And if the person doesn't have one? Also, the passenger list will be forwarded to the airline in advance. Issues? By land - issues? No exit procedure and assume person can travel to Mexico with just the passport.