How long would someone be on immunosuppression meds after a transplant?

Usually life long: Most transplant recipients need to be on immunosuppresive medication for the rest of their lives. In a small number, microchimerism may induce tolerance and allow the person to get off medication.

For the organ's life: The transplanted organ will never change its genetic identity - it will always be made of different dna than you. Your immune system will ultimately recover from the drugs you took, recognize the organ as "foreign" and reject it. Although a very small percentage of people can get away without taking the meds, we cannot predict who. For this reason, you must plan to take them forever.