It's the oficial reflow, so it will last "like new", or at least close to that? Like, for years?Are you talking an official "reflow"? Or the 'oven method'?
If the oven method, nobody can really say - it doesn't get near hot enough to truly reflow. It's a bandaid at best, and that may last a couple of days/weeks/months.
A true "reflow" is essentially redoing what happened during manufacture, and should last a fair time.