After migrating your classic Google Site to the new version, you can still access the original classic site. Google provides this option to ensure a smooth transition and to allow users to verify that all content has been correctly migrated before fully switching to the new version. When you initiate the migration process, Google creates a new site in the updated Google Sites format while retaining the original classic site. This means you have the opportunity to compare the two sites and make any necessary adjustments to the new version without losing access to the classic site.

However, it’s important to note that Google has set deadlines for the complete deprecation of classic Google Sites. Eventually, classic sites will be archived and no longer editable, so it's crucial to complete the migration and any necessary adjustments well before these deadlines. Keeping both versions accessible during the transition period helps ensure that nothing is lost and that the new site meets all your requirements before the classic version is phased out.

For further details and updates on deadlines and the migration process, you can refer to Google’s official support documentation and announcements related to Google Sites migration. These resources provide step-by-step guides and best practices for ensuring a seamless transition from classic to new Google Sites.