I had a discussion on this very issue with Radio, me being you and him being me.
I told him that it is obviously related to one's rate of loss and hair loss progression. Many lose hair in bursts- one that does not experience an onslaught for more than 2 years will of course keep his minoxidil results. Some people even stop receeding at one point.
Radio argued that the average person on minoxidil treatment(he mentioned a study) will start to experience a decline in one or two years, as this is the time that minoxidil regrowth can outrun the balding process.
I have no reason not to believe him.
Even if the 2 years average mark of decline turns out to be inaccurate, it is a fact that a minoxidil only approach is like trying to save yourself from drowning by pulling your hair up.
Minoxidil is a hypertrichotic agent. It will enhance growth where an active follicle is- either it is miniaturizing due to male pattern baldness or not. Minoxidil just makes you a bit hairier and has nothing to do with the balding process.
This point is very important given that minoxidil is marketed as a hairloss treatment. I have come to believe that it has nothing to do with male pattern baldness.
It think of it as the most natural of wigs.