Well, a proper raid group would keep both of them and work on the phase. Hypothetically though if it was a pug and someone had to be kicked then the one not doing the mechanics would be kicked. That's a pretty easy call. Anyone who would kick the person doing the mechanics and maintaining dps that is sufficient to complete the dungeon would be a moron. However, usually if someone is not doing mechanics their DPS will go down dramatically due to them being dead.
