I think if he was in danger of permanent damage, his signs and symptoms would be more severe than they are now. If you want, and are able to, you could get some things together, bundle him up and take him in now. If it would ease your mind.
It's normal for a parent to be in a state of shock in a situation like this. No one wants their child to be sick, let alone potentially with a life-changing condition like diabetes. But if you can talk to yourself about staying calm and avoid catastrophising, it will be much easier to get through it.
Most people I have heard of who have type 1 diabetes got diagnosed like this, ie they had days or weeks of thirst and hunger and other symptoms, and things got to a point where they saw a health professional and got a blood sugar test. It can be a surreal experience and it is a lot of information to take on board all at once, but the doctors and nurses will tell you what you need to know and things will be written down for you to digest slowly. This forum is also a great source of info and support, and if we think the health professionals are not being thorough enough we will say so.
If he has diabetes, you will have plenty of help coming to terms with it and helping him to get well and stay well. Things always seem more scary in the middle of the night. Tomorrow will bring some certainty and some peace.