There has been many an NFL player to undergo a serious injury, just as Dak has had. It's perfectly normal for them not to know what to expect until they've been back in action long enough to trust the durability of their injured part. Dak's been doing all he can to ensure his injured ankle being one that should hold up to whatever stress it might have to withstand. It's normal to have a healthy degree of fear before knowing what to expect. Dak is just a man, certainly not Superman, or anything of the sort. He shows no level of excessive fear.
Fear is a very positive impulse that helps to prevent a situation from overcoming anyone involved in an inherently dangerous situation. He'll eventually be taking hits that will test his ankle's durability. Hopefully, he'll come away from those threats in a relieved and relatively confident state of mind. I think he's more than resilient enough to hold up to such pressure, in the meantime. There are, certainly, no obvious indications to assume otherwise. QBs are exposed to danger on an ongoing basis. Dak has displayed an ability to deal with it. I think that will continue.