All of your USDC and market shares are securely held in a blockchain wallet. This wallet can only be accessed by the owner of the email with which it is linked. Polymarket has no access to these funds. All funds would remain in your wallet, and you will be able to retrieve them using your email address. You can read more here.
We use your email to provide you with an Ethereum Wallet that is unique to you. We can do this by using a third-party, trusted, and audited solution called Magic Link. Read more about their security here.