I have this same situation due to retiring in 2018. From what I heard last week, if you have not filed your 2019 tax return, the IRS will use your 2018 AGI to calculate the amount of your check. I was holding off filing since I owed money. When I heard this I immediately filed and the IRS accepted my return. This was 2 days before the bill was signed, so I think I am good.
