I have no idea what stage my mother is at and I don't really care - she has a diagnosis of Alzheimer's and needs support and that's enough for us. She still lives alone so obviously spends time on her own. She cannot use the kitchen appliances other than the kettle and the toaster and we have had a gas safety valve fitted on the gas cooker so she cannot have any accidents - pre-empting problems really as although we knew she was not using the cooker, we had no evidence of mis use. She only eats cold food now but we make sure she has a hot meal with us every day so that is fine, she has toast or cereal, snacks foods such as pork pies, sausage rolls or little salad pots and a lot of biscuits and cakes when on her own.
As we have security cameras in various positions around the outside of the house which link to our phones, we can monitor callers ( and talk to them) and we know that she does not wander - other than a daily visit to the local shops to buy a newspaper and yet more chocolate but she is home again within 20 minutes. No one can phone her unless I have input their number on a trusted list so she is safe from scammers and we can control her heating from our phones.
So far, we are happy with this situation, yes, she has dementia and cannot cope without support but she does not need 24 hour support although we know she will one day. Only you and your family know how your PWD would cope when in the house alone, it does not matter what stage they are at, there is not hard and fast rule. If you are not happy and feel that she is unsafe when left alone, then if you can provide that level of support, carry on, but if not, then it might be time to look at a care home.