For some types of cancer, you only have to be in remission for a few years to be cured -- for your chance of developing the same cancer (recurrence) to be no greater than people who have never had that type of cancer. For other types of cancer, like mine, the chance of developing it again will always be greater than if I'd never had it.
In 1993, some doctors advised me to undergo a bone marrow transplant with a new conditioning regimen (drugs used to kill the cancer before rescuing the wiped out marrow with stem cells retrieved from the bone marrow in the hip). Studies were promising, showing most patients' cancer going into a complete remission.
I declined, partly because nobody knew if these remissions would last. And the known toxicity could cause major long-term effects. Years later, studies showed no survival advantage for transplant patients.
I raised my hypothetical question to make a point: If someone discovered a cure for me while I was involved in a trial, I would leave the study and go for the cure. Patients' welfare is always paramount.