Here is some evidence that taking some time off doesn’t necessarily mean you will lose your fitness. Muscle memory broken down scientifically.
It took me more than five years of hard training to break 4:00 for 1500 meters for the first time. Not long after, I missed almost two years of training with a knee injury. When I was able to start running again, I wondered (and worried) whether it would take me another five years to regain my form.In fact, I was able to break 4:00 again after only a few months of track workouts and ended up running 3:48 that summer. How could something that was so hard the first time be so easy (relatively) the next time?
Source: Muscle Memory and Endurance