I've already written before that without Steve there's simply no Maiden... but I'll do my own list of band members importance, based also on the fact I really love both TXF and FotD...
1. Nicko - he's been co-creating the sound for so long he actually became the sound - while 'Arry's base has been less and less pronounced on the reunion recordings, Nicko's style of drumming let's you know you're listening to Maiden immediately. I have no interest listening to Maiden without him (and it also might show in my dislike for the first three albums, though it's definitely not the only factor)
2. 'Arry (I realise 'Arry's objectively and technically more important, being a bandleader and all, but I'm talking about the importance of members to the current sound)
3. Janick - I just like albums with him more than those without him. Considering the fact he has written the best song of the album for the whole TXF -> TBOS sequence (if we count Navigator as "his"), his departure would be very detrimental to Maiden as a whole, IMHO.
4. Davey - he's been in the band longer and he might be synonymous to Maiden in general... but current Maiden could continue much more easily without him than without Janick - mostly because the songwriting issue. They are still close to each other, though.
5. Bruce - though commercially probably the most important member, I personally wounldn't mind another X Factor, myself. Maiden can lose him and still sound firmly Maiden.
6. H - I like both albums without him and although I love his work on the reunion albums (the solo on Different World, his work overall on TBOS), I would still love Maiden if he went away and ditto as with Bruce - without him, Maiden is still Maiden.
I'd say 1-2 are the really indispensable members, 1-3 is essential if you want to keep the quality standard high, or at least as good as possible and 1-4 must remain for me to remain a real, heartfelt fan.
