If someone had a high strength reserve, is it possible to keep it with plyo work instead (12lbs medballs, bodyweight exercises, etc)
R3N3GAD3, good question. When you say high strength reserve, I am assuming that you mean high relative strength compared to bodyweight.
Are you asking whether they would be able to keep a high strength reserve for weightlifting movements, or for sprinting activities?
Yes, strength reserve in that context.
My question is aimed for all areas: weightlifting, sprinting, whichever.
Renegade
As for weightlifting, it would not matter if the athlete had a high strength reserve, the sportsman needs to continue to do the movements or he will lose sporting form. How long would this take? I’ll have to check my exiting and interesting soviet journals 
Seriously, though, the strength reserve will only last so long.
I choose to see plyos. med ball throws, etc as a display of power output, and not strength activities. Without the constant overload of the muscles, the body will eventually lose strength, regardless of the strength reserves present.