If the ban is temporary and gets lifted in 7 days or whatever the time is, the member can either keep using the newly created account or can abandon it. It can't be deleted.
If the ban is permanent, the member isn't allowed to keep using the new account unless it's to appeal the ban in Meta.
I think, those who use a new account will definitely have a lot of accounts, their latest accounts will of course be active when they already undergo a 7-day ban from the old account.