Taking the second issue first, that can't be known at this point. Back pain is a huge source of disability, and it is impossible to predict who will do well and who won't. I can give you some general ways to improve your odds of avoiding disability: don't smoke (smoking affects more than just the lungs!), keep your weight in the normal range, stretch and exercise three times per week, strengthen your abdominal muscles, and avoid things that put 'wear and tear' on the back-- such as lifting while bent at the waist, carrying things in outstretched arms (keep things close to your center of gravity).
As far as the pain pills-- I don't know if you are addicted to them, or if you are physically tolerant to them, or both. Medications like percocet are not generally hard on the stomach; the things that hurt the stomach are the 'NSAIDS' like aspirin, ibuprofen, naproxen... 'percodan' contains aspirin would be worse on the stomach than 'percocet', which has tylenol. Tylenol-containing meds in excess can harm the liver, but that would not cause blood when you throw up-- it would be painless, but eventually require a liver transplant or cause death.
If you see red blood when you vomit, you are likely seeing blood from small tears of the esophagus called 'mallory weiss' tears-- these can be dangerous in people with cirrhosis from chronic alcoholism, but otherwise don't usually cause significant problem. If the amount of blood is large, of course, you should seek medical attention. Bleeding from a stomach ulcer will usually appear as 'coffee grounds' when you are sick-- the blood takes on that appearance from exposure to stomach acid. In the stool, blood from the stomach will look like 'tar'.
Opiate addiction is characterized not so much by the initial withdrawal symptoms, but by repeated cycles of use, quitting, and relapse, that usually demoralize the person over time. If you end up in that position, I encourage you to seek help from either the 12-step community or a residential treatment program. Some people can 'get clean' with outpatient treatment, but the odds improve significantly with residential treatment of over 90 days.
JJ
i forgot to say i wrecked my back about 4 years ago and i was being perscribed percs for about 6 months. but my back is still not taht great and i have chronic pains. i cant even go to a bar and stand for a hour with out needing to sit down. will pain be a problem?