This is something that comes up from time to time and you see it asked occasionally in forums. Severs disease, or what is more appropriately called calcaneal apophysitis as it not a disease, is a self limiting condition. The child will always grow out of it, so its is a reasonable question to consider.
Obviously if the pain is causing a problem, then yes, cut back on activity levels, use ice after sport and maybe use a cushioned heel pad. If the pain is not that bad, then simple load management, ie using activity levels that are within tolerance maybe all that needs to be done. It then becomes a case of managing lifestyle and expectations and waiting for the natural history to run its course.
Episode 28 of PodChatLive addressed all the issues around calcaneal apophysitis: