so Nintendo said in march 2023 they are shutting down the 3ds e-shop, will I still be able to use Pokemon bank once my subscription runs out?
Yes, you still can.
Pokémon Bank is to become completely free after the EShop shuts down.
In late March 2023, Pokémon Bank's paid passes will no longer be offered for purchase, at which time Pokémon Bank and Poké Transporter will no longer be available to download. On the same day, Trainers will be able to start using Pokémon Bank at no cost. There is no end date planned for this no-cost service.
In late March 2023, Pokémon Bank's paid passes will no longer be offered for purchase, at which time Pokémon Bank and Poké Transporter will no longer be available to download. On the same day, Trainers will be able to start using Pokémon Bank at no cost.
There is no end date planned for this no-cost service.
Source