yeah there should be a cover there, but its not a massive deal if missing. certainly wont fail the mot like that. its there to stop things getting into the bellhousing, if say a bolt fell in there it would get mached into the gearbox by the flywheel, and since box is aluminium it would loose vs steel bolt! also stops clutch contamination if oil got in, but it would take a large amount to get in there and get on the friction disc, as it would mostly just drain out the bottom, plus the friction disc is pretty well covered by the fly and pressure plate.