@Shanghai101 I have studied EDs and worked with patients. It is hard to say. All the evidence points towards early intervention offering the best chances of a full recovery - but that isn't to say that those who have been unwell for a long time can't recover. Lots of people who have suffered from EDs go on to live happy, healthy and recovered lives. However, a large proportion will remain in a quasi-recovery - in that case we look at improving their quality of life as much as possible, keeping them stable and able to reach their potential as much as possible. Then there is another portion who remain very unwell and aren't able to live what we would call a 'normal' life. Lastly, there are those who die as a result of the illness.
As you all know EDs are incredibly complex and no two cases are the same. Whilst poor nutrition and weight loss exacerbates symptoms and worsens behaviours, many do have underlying causes. There is no one cause, but a collection of 'predisposing, precipitating and perpetuating' factors that contribute to the development and maintenance of an ED. Experts and therapists differ on their approaches - but ultimately the sufferer needs to find something that makes them want to get better. Even if it is something very small. Sometimes this will be a 'revelation' to the person and they become very determined to recover in a short space of time, on other occasions it is a gradual realisation and very small steps.
As for advice to families - don't give up on your loved one and try not to compare to others. No two recovery journeys will be the same. Also accept that there will be set backs - recovery isn't linear by any stretch of the imagination. The important thing is learning from set backs and putting things in place to overcome them and prevent them happening again in the future. Also, there is a lot of chat about being overly cautious when they seem to be doing well in recovery - I would take this as a good sign. Lots of people with eating disorders struggle with the fact that the support goes when they look better, even though they haven't recovered mentally. Letting your DC know that you are still there for them is really important in recovery.
I know on a previous thread there was a link to Orri, I don't work there but really admire their ethos. They do webinars which are open to healthcare professionals, carers etc and I would recommend attending them or catching up on vimeo afterwards.
I would also say check in with the immediate environment - probably something you are all doing anyway - but remove, or at least try your best to prevent, triggers. Things like friends and family mentioning anything about weight, diet, calories, 'treating themselves to pudding', 'skipping breakfast', 'lots of food' etc. Also make sure no one tells your DC they look better - this will always come across as 'bigger' to someone with an ED.
Be mindful of their friendships groups too - this can be tricky as your DC may be embarrassed about their illness and not want to discuss. However, teens talk about weight, weight loss and diets so it can be like throwing a sufferer into the lion's den. Obviously you can't shield them forever, but it is about trying to remove triggers whilst they are most vulnerable, then establish coping mechanisms when they are stronger.
I would also suggest encouraging your DC to think about their futures and what they want to achieve in life. Where do they see themselves in 10 years time if they recover? Then ask them to think about it if they still have an ED. Explore non ED related short term and long term goals that give your DC something to hope for outside of the narrow world the ED has created. You want them to start to establish an identity where the ED doesn't have any kind of role.
I have followed these threads out of interest every now and then - but obviously it is unethical to give individualised advice online. The above is all general guidance but I hope it helps you. I wish you and your DCs the best of luck with your recovery journeys.