To answer your question, Nintendo can ban your console without touching your account. This way, you can retain all of your purchases and funds but still be hit with the ban hammer. Account bans are rare because of the possible consequences associated with them so they are limited to severe cases. You can still buy and download stuff from the eShop if you are hit with a console ban only. Just go to their website, download whatever it is you want, then select "Update Download Progress" from your console and it will begin downloading.