I've drove without the sidesills several times to the muffler shop. I made the mistake of telling the muffler shop what the sidesills cost, but I had to remove the sec. cats anyway, as he wouldn't. Watch your leg getting out of the car, it'll third degree your leg.
At the time I had the skid plate, complete exhaust system, and side sills off the car. You would be amazed how much the chassis flexed while driving. Those three things off the car made it obvious how much of a part they play in chassis rigidity.
Skip White