Let him play, learn and get experience. We need to find out if Dak is the future. If he looks like he is the future, Garrett needs to be replaced, and get a real Coach with an offense that can be tailored to Dak, with a real QB coach. I don't see a reason to keep Dak in an offense only Romo can run. Let Romo and Dak fight it out in camp. Romo will be gone sooner rather than later, and Garrett has proved he can't win a game without Romo.
If there is any chance of ruining Dak, it is Garrett and his Romo only offense that will do it.