although it will last for life, you will probably require more eventually because you non-transplanted hairs that are predisposed to falling will continue to fall and you will need to fill those gaps in.
propecia helps make that slower... but eventually, it will still happen... hair transplant is a choice to make, if want to always have a head of hair and can commit to paying for further work if needed. I personally have committed to that and am very happy after my first hair transplant.