If you go off the drug, you regain your weight. If you go off your diet, you also regain the weight. That, then, is a wash.
These drugs currently cost a fortune, so lifelong dependence is an expensive scenario, especially since most insurances refuse to cover them. On the other hand, this is preventative medicine, which might significantly reduce costs from obesity-related health issues down the road, including heart disease, cancer, and arthritis.
Compliance with a weekly injection is also likely to be higher than compliance with a long-term dietary change. Of course, since something like 95-plus percent of diets fail long-term, almost anything would have a higher compliance.
I don't know that we have enough data on long-term use of these drugs to be confident about long-term side effects, either.
I don't love the idea of being dependent on a medicine for the rest of my life, but there are plenty of other lifelong medicines that we just sort of accept as normal now. Insulin-dependent diabetics and people with high blood pressure are just two examples.
I guess for now I'm putting these in my "cautiously optimistic" bucket.