A very high electrical field, over a couple of years, or another neodymium magnet held at close range of similar strength will have an affect. If the magnets can not get "away" from each other they will cause each other to weaken.
Since the actual output of a similar Nd-Fe-B magnet will not be very close to the intrinsic coercive field of the material [a measure of the magnet materials' ability to resist demagnetization], it is unlikely that such a magnet would permanently demagnetize another. However, while in the presence of the second magnet, the first magnet would experience a temporary partial demagnetization. How much, and to what extent, would be dependent on, as DrDick says, the magnet geometry.
A hydrogen-rich environment would cause catastropphic phyiscal changes in Nd-Fe-B magnets within a matter of days or weeks, rather than years. Put it under pressure and you'll see decrepitation of the alloy within minutes and hours. It's one way they use to refine the raw powder used for Nd-Fe-B magnet production.
