No, Nicko will not be Maiden's drummer on any future studio material. His ability to perform at the level he and the band require and are accustomed to has been affected by both age and the effects of his stroke. Those chops will not return. There are patterns and strokes he simply cannot play any longer at tempo.
Read the announcement again; Rod clearly says how much the band will miss him and that he'll always be part of the family. You don't miss someone whom you plan on spending time with in the studio. It's done.
As for future guest appearances at any live shows, doubtful. Leaving the band after forty-two years is like leaving a marriage. You don't want to see your ex getting along with the new guy...and in the case of the band, they're going to want to make the new drummer as comfortable as possible so he can give his best performance. Having the musician you replaced hanging around isn't conducive to fostering such an environment.
Its time for Nicko to enjoy his family and his life. Once you break that routine of recording/rehearsing/performing/traveling/practicing/exercising to stay fit and in his case, intensive therapy to try to regain your ability, it's impossible to just get up onstage at a show as coordinated as is Maidens and just bash out "The Trooper" for old times' sake when you couldn't play it properly when you left.
