Well your situation is unusual and unfortunate. All you can do is mail in the 2020 return and another 2019 return and wait. Make sure to mail them SEPARATELY and have some sort of tracking put on them so you know they arrived.
As for the next stimulus payment (an advance of the 2021 credit) just like the last 2, if you do not get it in advance then it will be a credit on the 2021 return you file next year.
