We're getting Fallout 5 at the absolute earliest in 2030, but even that is highly unlikely, 2032 is a much more likely year for it.

Meaning a 17 year gap between 4 and 5. When Fallout 5 is out that's that, it's over. Bare minimum 15 year between these two games. Fallout 2 and 3 was 10 years and the franchise was considered dead in that gap. This is modern gaming