Shaggy, I have to disagree with some of your points. First I don't believe that "most" coasters have special seats or restraints for disabled guests. I think it is great that some coasters do, but I think overall most coasters will not allow a person with two amputated legs to ride. Both of your legs make up something like 2/3 of your total body weight. This puts your center of gravity around your waist. With both legs missing, your center of gravity moves up to somewhere in the center of your chest. Rides are just not designed to accommodate that, and a rider without both of their legs can be thrown from the ride.
Second, I know evacuations are rare, but how does a rider climb down a 200' lift hill if they don't have any legs? Most parks don't allow their ride ops to help lift disabled guests in and out of the trains. So, I highly doubt that they would carry a disable guest down a lift hill.
So I think the answer is that it depends on the park and it depends on the ride. Anyone missing limbs should check with the park's customer service office and see what the park allows.
