There would presumably be new people developing the disease they'd found a cure for, so there would still be ongoing business there. It's true it probably wouldn't be as lucrative as providing medication you can never stop taking, but it could still be quite profitable.
If the startup went out of the "providing a cure" business, in a free market, another hungrier startup would take its place.
There are quite a few businesses that don't have regular, ongoing customers. Home builders, colleges, funeral homes, boat sellers, etc. often provide a product or service once per customer and move on to selling to other customers.
There would presumably be new people developing the disease they'd found a cure for, so there would still be ongoing business there. It's true it probably wouldn't be as lucrative as providing medication you can never stop taking, but it could still be quite profitable.
If the startup went out of the "providing a cure" business, in a free market, another hungrier startup would take its place.
There are quite a few businesses that don't have regular, ongoing customers. Home builders, colleges, funeral homes, boat sellers, etc. often provide a product or service once per customer and move on to selling to other customers.