I would not be interested in playing that hypothetical knight situation. I like to have a full character, and not just the stick that another player hits people with.
As for unconventional D&D TO&E's, one of my games is a Wizard, a Sorceress, and a Rogue. We still meet the tactical roles, but mostly because the wizard plays up close and personal as a consequence of our lack of close-quarters characters.
Another game I played in was fighter-fighter-rogue. This worked out well, even without magic support or healing, because we had some serious and very consistent damage output.
Most of my non-D&D games I run don't have healers, but that's because in most of them healing is fairly weak and everybody can carry a first aid kit to help get people back to a medical facility after a machine gun repaints the walls with their blood.