Not any time soon. Microsoft may choose to not support it after 2026, but it will likely still work for legacy sites. It is not the preferred option when creating new sites in SharePoint Online in M365 as the modern interface is mobile-friendly and uses newer underlying technology. Ultimately, you can toggle between classic mode and modern mode for individual SharePoint pages, so the modern interface is not really a direct replacement of the classic interface. It is simply another way to show your pages in SharePoint (and make them mobile-friendly).