Generally speaking, you can explore any bit of any map whenever you feel like it (choose a route based on a “spawn site” that is in the vicinity of the area you wish to explore and then manually intervene to go where you want).
The intention of the proposed “save without exit” feature is not that you can save mid-route, exit, and then “reconvene” on that same ride where you left off at a later date but instead is intended to allow one to swop between routes/worlds, saving each ride individually, without having to exit the game entirely.
If you are seeking to earn the route badges, these (correctly so) need to be earned by completing the route in a single ride - and I expect (hope) this will remain irrespective of when we eventually get the ability to save without exiting Zwift.