Furry I think the concerns that people have about this WoE in the long-term tend to be rooted in the current "healthy eating" advice of fat is bad. It's well worth reading up on the history of healthy eating advice, for example Nina Teicholz's Big Fat Surprise or Gary Taubes's Diet Delusion or even more damning, his Case Against Sugar which is meticulously researched and more than half of the book is taken up by references.
One thing that is for sure is that obesity itself is a risk factor for diseases such as diabetes, coronary heart disease, stroke, cancer and Alzheimer's. So if you have lost weight and gone from overweight/obese to a normal weight then you have undoubtedly reduced your risks of disease.
The main worry is cholesterol, as ChocDog mentioned. It's worth bearing in mind that there never has been any scientific evidence that cholesterol intake has any effect on health (apart from in people with familial hypercholesterolaemia which is a genetic condition). The initial idea of reducing fat intake was based on a hypothesis in the 50s/60s and it has not yet been possible to prove the hypothesis that saturated fat intake is related to the risk of coronary heart disease. The Women's Health Initiative study found that lowering fat intake made no difference to the risk of heart disease, stroke, or colorectal cancer. This is a particularly famous study because it discovered that hormone replacement therapy increased the risk of breast cancer, heart disease, and stroke, and it made headlines at the time because they had to stop the trial early. Long story short, even when studies are designed to prove that reducing fat intake improves health, they couldn't do it.
One potential problem with eating low carb in the long-term is with thyroid hormones. People with hypothyroidism need a slightly higher carb intake (above 50g per day) and may not be suited to a very low carb or ketogenic diet. Key signs of low thyroid hormones are feeling cold all the time and unusual fatigue.
For a bit more information about the long-term effects of LCHF take a look at the Diet Doctor's health markers after 10 years.