This is impossible to prove as this will differ from one individual to the next. RCH-01 can only give your Androgenetic Alopecia hair the DHT resistance that your donor hair has which will vary from individual to individual. Some people thin in the donor area too, especially into old age. So if your donor region was genetically susceptible to start balding in your 70s, then your RCH-01 treated hair would suffer the same fate since it's the same cell line.
IMO, donor hair is not immune to DHT in anyone. It is just highly resistant and this resistance can vary. Given a long enough time line and high enough exposure to DHT, donor hair will also begin to experience the same adverse effects that hairs in the Androgenetic Alopecia region undergo. Similarly, given the presence of DHT, all men will eventually get prostate cancer. The ones that don't just happen to die from something else first.
So, people asking/thinking finasteride won't help after RCH-01. Does finasteride thicken hair in the donor(I believe it does and many hair transplant surgeons would affirm to this)? Why would it not? If yes, then finasteride will still help after RCH-01 however, you would probably die before you would actually see the benefit. If people lived for centuries, then I think finasteride would be a must along w/ RCH-01 in order maintain a full head.