When I saw Maiden live a couple of weeks ago I could feel Nicko struggling. Most bands, regardless of genre, see their drummer replaced once they reach a certain age. Playing drums is just too taxing. I think someone conducted a research and came to the conclusion that Blondie's drummer, during one gig, had the same amount of physical exertion than a pro footballer does. And bands play more often than footballers play... However, seeing Maiden without Nicko would be akin to seeing the Beatles without Ringo - Nick's personality as a musician came across in their sound, and gave them their identity. A new drummer will sound good but it won't be him.
I don't know if this is going to have an effect on Maiden's career, in the sense of them recording more new material or not... The rest of the band are younger but not that much younger - Bruce himself will be 68 when the tour's done.