It can be used forever if you want, or you can do it temporarily I imagine. It really depends on what you want to do though. If you feel better doing the omad diet forever, then I say go for it. If you can keep up with it, may as well.
But if you want to just lose some weight and go back to 3 meals a day, that's always an option for you.
For me, I think I can see myself doing OMAD for life.
There are a lot of health and anti-aging benefits that come from fasting, at least part of the day, and giving your digestive system a chance to rest and recuperate overnight, or even longer.
I noticed that some people vary what they do, and the have one meal some days, and 2 meals other days, as well as 1-2 days of fasting.
It seems to me that OMAD is something that is more of a lifestyle change than just a temporary diet, although I can see that it would be fine for just that purpose, too.