Three-legged pets are usually called tripods - or even tripawds - and are actually incredibly resilient animals despite missing a limb. All animals are highly adaptable, and tripods are no exception. They can go about their lives as if nothing ever happened. Owners who own a tripod pet often forget their furry friend is even handicapped to begin with.
However, there are some important things to keep in mind in order to help your three-legged pet along the way. Watch their weight so they can easily manage equal weight distribution. Tripod pets are especially at risk of arthritis. Get them a super comfy bed while you're at it! Any pet wouldn't like to lay on a hard surface, but tripods are also at risk for developing hygromas in their elbows, and a comfy place to rest will help ease that.
Be patient with them on stairs, and install a ramp if possible. Because cats especially love to climb and perch, you shouldn't take that joy away from them if you can help it. Taking care of their paw pads is also essential, as is with any pet, because their feet take all of their weight. Finally, if your pet is old enough, investing in a wheelchair or stroller if they're no longer mobile will greatly boost their spirits.