story-wise you definitely need to lose korgan, and mazzy is a perfect companion for a paladin. and it's more of do you want to lose korgan or aerie.
aerie is fine as your only cleric. anomen's an ass. keep in mind that once you rescue imoen someone else will have to leave, but with your current party (incl the mazzy substitution) that won't be a problem. (no spoiler here!
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