If you take Minoxidil and experience regrowth, and then start taking Finasteride to block DHT, will you still lose the Minoxidil regrown hair if you stop using Minoxidil?
In most cases, yes. The hair that you regrow with minoxidil is not necessarily going to be sustained by finasteride, and vice versa. In some cases it might stay true, but generally you can consider some hair to be "minoxidil hair" and some to be "finasteride hair".