I think a lot of you get far to worried about how long the band will stay, Pata & Heath clearly love being in the band and I havn't seen them suggest anything otherwise, Sugizo will stay there to support the band and hide for as long as the band stays alive, as we all know Toshi gave lots of "I'm back I'm finally back!! I'll sing for everyone and for X until I'm at least 60!!" speeches at his last concert. Will Yoshiki damage his neck/back even worse at the Nissan concert? I don't think so, they have a variety of songs including the new ones which feature much less harder drum work, even if it being an outdoor concert brings back a classic song like Blue Blood/Silent Jealousy, they still have songs like I.V and all the ballads, he'll be fine.
Yoshiki said in some recent interview "I think my body will only last for four years, I'm heading towards destruction (drama queen ect.)" but as for this being the last concert, or even tour, I don't think so, it'll be a while yet before the band dispands again imo.
Also, apart from Yoshiki (unless he's actually careful about what he's doing), age has no affect on how long a band lives for, just look at Iron Maiden, Judas Priest, Heaven and Hell ect.