newacct

When you leave the US, you cease to have any status, and any Extension or Change of Status is abandoned (it is moot anyway). When you re-enter the US on the basis of your valid H4 visa, the officer should admit you from scratch for the same duration as the H1b I-94, regardless of what you applied for during your last stay.

I don't understand what you mean by "file a derivative I-485 on my behalf". Are you filing a second I-485 for yourself when you already have an I-485 for yourself pending?

Your dependent cannot get TD status as you no longer have TN status. They can stay in the US for as long as their AOS is pending.

It depends on when is the first month when the date in the Final Action Date chart passes your priority date, and what her CSPA age (i.e. her age minus the length of time the petition was pending) will be on the 1st of that month.

If she filed I-539 before her status ended, and she left the US while the I-539 is pending, she is fine. I don't see any reason why she can't come back. She should bring her I-539 receipt.

I am assuming that she is not in H1b/H4/L1/L2/K3/K4/V status. If she leaves the US while her Adjustment of Status (I-485) application is pending, she automatically abandons her I-485, unless she had been granted Advance Parole before leaving, and she returns on that Advance Parole.

No. You are not out of status. Your I-94 shows the H1b status you were admitted on and the date you were admitted until. However, not working on H1b status could eventually make you out of status. (There is a 60-day grace period for people who leave their jobs, but I am not sure what happens with people who never started their job.) Yes. You can start working before you receive your SSN. You can complete I-9 before you receive your SSN. (If your employer uses E-Verify, you can still start working before your receive your SSN if you have already applied for it. I am not sure about what happens in the case where you have not been able to apply for it.) See this brochure from the SSA: As for completing the I-9, see the I-9 instructions: For E-Verify, also see this page of the E-Verify User Manual:

It is "legal" for L2 spouses to work without an EAD right now. However, current L2 I-94s will not serve as proof of work authorization for the I-9. So if you are working as a regular employee where I-9 is needed to start work, you will still need an EAD (until new I-94s specifically indicating L2 spouse are issued).

Yes. See this page from USCIS and this page of the Handbook for Employers.

It depends on what the Resident Since date on the card is.

If you are a green card holder (i.e. permanent resident), your status is not dependent on anyone else's status. You have the right to stay in the US permanently. You do not have to relinquish your status (unless of course you want to). If you are a conditional permanent resident with a 2-year green card, you can apply for Removal of Conditions yourself now on the basis that your spouse died.

Yes. She can use that visa to enter the US on any day up to Dec 31, 2021, or even enter on Dec 31, 2021 itself.

Her I-539 was automatically abandoned when she left the US, since one does not have status while outside the US, so she has no status to extend anymore (and approval or denial would make no difference anyway). She can get an H4 visa on the basis that her spouse has H1b status. What status she had on her previous stay and whether she applied to extend it is not relevant (other than to show that she did not accrue unlawful presence).

The main issue is the continuous residence requirement. Although an absence of between 6 months and 1 year creates a presumption of interruption of continuous residence that can be overcome with strong evidence of ties, an absence of more than 1 year definitely interrupts continuous residence that cannot be overcome. (There is a narrow exception for people working abroad for the US government or US research organization, who can file N-470 to preserve continuous residence during an absence of more than 1 year. I will assume that that does not apply for your case.) Since your absence in 2016-2018 was more than 1 year, your continuous residence was interrupted, and you need to start over from 0. The question is how long you have to wait before you are eligible to apply for naturalization. I will assuming that you will be applying under the 5-year rule, and not the 3-year rule for someone married to a US citizen for 3 years. According to the chapter linked above, if you had strong evidence of ties that would have been enough to overcome the interruption of continuous residence if you had been absent between 6 months and 1 year, then after your absence of more than 1 year, you need to wait 4 years and 1 day after your return before you can apply for naturalization. If you do not have such strong evidence of ties, you need to wait 4 years and 6 months after your return before you can apply for naturalization.

Not sure what you mean by "180 days deadline". Your I-539 was applying for an H4 Extension of Stay or a Change of Status to another status?