A picture would help to see the exact arrangement, but if the switch is the regular side-wired type then it should have only one wire under each screw terminal. Other splices will be made in the back of the box with wire-nuts (or possibly crimps or some other method if it's an older installation).
Assuming just two wires to the switch itself (one on each terminal), then you could safely remove the switch by capping each wire it with a wire-nut. Or if a wire is just a pigtail into a wire-nut splice behind, you can remove the pigtail and just reconnect the other wires.
If you have a regular double box for the existing switches though, you might have trouble locating a replacement switch plate which has just a single switch cutout on one side and is blank on the other. I don't recall seeing them in any of the major manufacturers' lines, but they might be available.
Converting to a single box would involve reworking the other wiring, and obviously would leave a large hole in the wall to patch up, but then you could use a regular single switch plate.