@XCross -- (1) when you leave the USA, your work visa is terminated and therefore you become a Non-Resident Alien thereafter.
(2) so for the year 2020, you will be a Dual Status taxpayer thus:
(a) you file a form 1040 covering your world earnings for the period Jan 1st through the day your visa is terminated / you leave the US soil
(b) you also file a form 1040-NR for any US source income for the rest of the year and in any subsequent years that you have income from the USA
(3) NOTE -- when you work on foreign soil for an US entity ( for example your current US employer pays you as a contractor but you perform the work in foreign country ) your income is sourced to the foreign country -- it is NOT US sourced income. Therefore USA cannot tax this not can your employer issue a 1099 to you, even if you have a SSN.
If you need more help on this. please let me know
