Because there is a monthly fee to keep the card active the card is automatically closed if you have a zero or negative balance for a few months in a row ... this is standard practice for any pre paid debit cards and is in the user agreement that came with the card. If it wasn't you would have to keep paying every month for the right to keep the dormant account open.
Now the good news ... if the deposit is made to a dormant account and gets rejected then the money will be returned and be reissued as a check to the address on the last filed return. If you don't get the money by 1/20 then you will get it on the 2020 return you file next year.
Hot off the press ... straight from the horse's mouth ...
https://www.irs.gov/newsroom/treasury-and-irs-begin-delivering-second-round-of-economic-impact-payme...
