How would you design a rescue mission for MarsOne colonists?

Rescue from an accident on the way there would just consist of putting enough fuel and supplies on the vehicle to have it fly past Mars and boost back on an intercept trajectory with the Earth. There would be no faster way to return.

Rescue from an accident on the surface would necessitate having a vehicle that can lift off from the surface under its own power. This is basically just as difficult as if the entire mission had been planned as a crew-return mission from the start, and would defeat the whole point of reducing costs by making it a one-way mission. Even the best possible case would be to land the return vehicle with its fuel tanks empty, and hope that the crew can extract enough fuel from the martian surface using solar power to fill the tanks before an accident happens. The return vehicle would still be enormously heavy and cost a huge amount to send.

Since going to Mars on the pathetic budget available to MarsOne is impossible, it follows that any "colonists" would actually be confined to a dummy "habitat" on a Hollywood backlot. If they needed rescuing from the predators in the advertising agencies and other shady characters promoting this folly, I would assemble a "sort of" swat team, with natty outfits and a camera unit, armed with suitable sponsors, and send them in at night to do a nighttime raid on the "habitat", effecting the "rescue" in fine style, fully documented, and by appropriate leaks there would be a bit show with riot police on the scene. The resulting documentary would be very profitable on reality television in prime viewing time.

Cheers!

Just pay SpaceX to figure it out. It's pretty obvious they're the only company with ideas or skills in spaceflight at this point.

Even if we got them back to earth, I feel that we'd never be able to rescue them from the bad decision making that got them there in the first place.

send two landers/rockets; instead of one.