I don't doubt that a 'reaction/reflex' goalie will lose reflexes as he ages, but it's not like 'positional' goalies won't either. The skills they rely on will be diminished as well so I don't know where the worry about one style over the other as they age comes from, unless there's been some study done that I haven't seen that shows it. Otherwise I think you can probably cherry-pick examples from both sides, and then there will be some sort of hybrid style as well.
Basically I don't think you can say Reimer's style will deteriorate worse with age than Bernier's or another 'positional' goalie simply due to the style.