I had cataract surgery and do not need reading glasses anymore. will this result last "forever"?

As long as life: I am guessing you had multifocal lenses put in at surgery which allows vision at far and near. Provided nothing else goes wrong with your eye, this result can last the rest of your life. Your eye is still susceptible to other conditions that can affect vision like macular degeneration which is independent of cataract surgery. Enjoy your new and exciting vision.

Hopefully: Sometimes refraction can change (effective lens position shift right after surgery) or scar tissue like posterior capsule opacification can occur.

It should: You are probably a little nearsighted or have favorable astigmatism. In all likelihood, this will last.

Maybe: A patient's vision after cataract surgery usually does not change so long as there is no health problem affecting the retina or cornea.

Probably: If you are healed completely after cataract surgery, your vision should remain the same from now on unless you develop other eye issues (such as glaucoma, macular degeneration, etc).