Statemint has an Existential Deposit threshold of 0.1 DOT.
Say an account holds some amount of asset X, and transfers away all its DOT so that it goes below the ED.
What happens to its holdings of asset X? Are they lost forever?
What if a new DOT transaction (above ED) brings the same account back to life? Does it still hold the same amount of asset X, or is it 0 now?
The DOT transfer that empties the account will simply fail.
First, an asset places a consumer reference on an account:
frame_system::Pallet::<T>::inc_consumers(who).map_err(|_| Error::<T, I>::NoProvider)?;
When one tries to transfer DOT, the Balances pallet checks if it can remove a provider reference:
let allow_death = allow_death && system::Pallet::<T>::can_dec_provider(transactor);
Finally, that function ensures there are no remaining consumers of the account's existance:
a.consumers == 0 || a.providers > 1 // <- returns bool
