Marketo Sync with Saleforce is based on the username, password and token. As soon as you change the username, the new token name and new password has to be provided for sync to start in Marketo.
Remember, if you reset the Salesforce.com password a token is issued and emailed to you therefore, the Marketo credentials will change ( u do it manually from "admin") to start the resync again.
To answer your question, the Marketo Sync will not work!