https://www.reddit.com/r/Flights/comments/12ogjho/what_would_happen_if_a_domestic_us_flight_was/

First, flights (to/from PR and Alaska) diverting to another country is a very rare occurrence, as for Hawaii, I couldn't find any record because there's only pacific ocean between U.S. mainland and Hawaii.

Second, If it's a quick diversion, you'd stay on the plane, you're not entering another country, the plane then take off again as if nothing happened.

Third, if you need to get off the planed, you'd likely have to wait on the tarmac or in a secure area of the airport, you are not considered "entering" that country because you aren't going through their customs. Especially with U.S. domestic passengers without their passports, as we saw this incident lately https://x.com/ParissAthena/status/1821287026009747670 .

In conclusion, based on the comments from the 1st link above, under all these scenarios, you would not go through U.S. customs when you fly back to the states, because these still considered domestic flights.

Note: I could be wrong, I'm not a lawyer, I just did my research online. And I doubt if many lawyers know about it 100%, because these are very rare occurrences. And I have met some underqualified lawyers and they just want your money.