It is virtually impossible to remove all glandular tissue. This means that it could come back. Usually, it does not.
What this means is that for the rest of your life you would want to avoid taking medications for which breast enlargement is a possible side effect. I've heard that there are over 200 medications which have Gynecomastia as a possible side effect. You'll have to be an avid reader of the material that comes with your prescriptions in order to avoid them. In many cases, there alternative medications with a different profile of side effects.
As you age, avoidance becomes more difficult since medications used to treat prostate enlargement are high on the list. some drugs used to treat Hypertension are also high on the list. Medications used to prevent or treat balding are the worst offenders.