I don't think anybody wanted Orga to die. I among others expected him to die, but that's not the same as wanting. Mika doesn't feel like a wholesome main character by traditional standards as he is currently, which Orga dying would have possibly fixed. However, by now it's quite clear this isn't a perfectly ordinary story anyway, so perhaps having Mika in his current state till the end wouldn't be a bad thing. I do know for sure I'd miss the weird interaction between Orga and Mika should Orga disappear, and it would be in no way compensated by developing Mika into a more traditional main character.

Having the main character split into two characters isn't such a bad thing when it's made to work this nicely. Orga is the dreamer, Mika is the maker.