In general it depends. If you modified existing blood cells genotype then it wont persist indefinitely. You'd need to modify the bone marrow. But then some cell lines work like you posed in your question.

Because this therapy edits the stem cells that are found in the bone marrow, it essentially means that the disease is being fixed at the source. Bone marrow stem cells eventually turn into blood cells and immune cells. So if 100% of the cells have been edited, then the resulting cells they turn into will be the edited type.

That is the goal but not that simple.

In most cases, the original disease-causing stem cells are effectively eliminated by the conditioning regimen (high-dose chemotherapy and/or radiation) used before the (autologous) transplantation, so they do not regenerate and cause further harm to the patient. However, in some cases, residual disease cells may survive the conditioning regimen and persist after transplantation, leading to disease relapse. This is more likely to occur in patients with aggressive or refractory disease or in those who receive a mismatched or haploidentical donor graft. To prevent disease relapse, post-transplantation maintenance therapy, such as immunosuppressive drugs or targeted therapies, may be used to eliminate residual disease cells. Additionally, close monitoring of the patient's blood counts and immune system function can help identify and manage any signs of disease relapse.