The answer depends on the type of pipe and the extent of the damage from the roots. If you have cast iron piping, typically you can remove the roots with a professional cleaning with a camera inspection when the job is done. If you don't know what type of piping and the condition of the piping, you can have the camera inspection done first. This will then tell you the amount of infiltration by the roots and if the roots have cracked any piping. If the roots have not cracked any of your piping, then a set of double knife blades on a main 3/4" cable will clear the line. It may take some time with heavy root masses, but it can be done. If your piping is of clay, you may have some damage. The clay piping was installed in the early 1900's and typically has a 75 year life span with roots as the cause of the breakdown. In any piping system that is connected with joints, except the new plastic solvent weld piping and the fiberglass liners, the roots will penetrate the pipe at the hub and the spigot end of the pipe. This is due to the water that seeps out of the joint on the bottom. Roots follow this source of water and then enter the pipe along the course of the water. Once a root gets into the joint, no amount of cleaning will remove it, because the joint is the only part of the pipe the snake can't touch. It is a 3 - 4" space that is generally filled with a joint material, sometimes rubber gasket, tar or mortar, depending on the material. The only way to temporarily remove the roots is to use a root destroyer after a rotorooter cleaning. This will kill the roots to 12 inches outside the pipe. Again this is only temporary as the roots will grow back as long as the pipe is leaking.
You don't always have to replace the pipe, you can have a liner installed in the pipe which will prevent the root growth. You should clean and kill the roots first so the pipe is empty, but the installers should take care of that.
If your pipe is made of tar paper (called greenberg) which was installed in the 40's during the war (because of lack of materials) then you will have to have the line eventually replaced.
Having a camera inspection is the first step, you can then show the tape to any one who is quoting you a price.
Raymond VinZant Plumbing Prof.