Deleting your account
What deleting erases, and the two things to settle first.
Deleting your account is app-only: Profile → Account → Delete account. It takes a double confirmation, the second button reading Delete forever, and it is permanent and irreversible.
What is erased
Your profile, collections and their folders, every card in them, decks and deck folders with their cards and history, tags, views and view folders, watchlist, price alerts and their events, your collection value history, scan history, build sessions, push tokens, and every cloud backup snapshot.
The Ledger goes too: sales with their buyers, batches, orders and lines; purchases with their vendors, orders and lines; and loans with the people on them.
See the Privacy Policy for what that means in legal terms.
Two things to settle first
Deleting your account does not cancel a subscription
Store subscriptions are managed by Apple and Google. Cancel Silvane Pro in your App Store or Google Play settings first, or the store may keep billing you.
Export a portable .silvane backup first. It is the only copy you will
have afterwards. See Backups.
Afterwards
The app does not sign you out into nothing. It says "Everything was removed. You're starting fresh as a new guest." and carries on as a new guest.