What happens if you gain weight again after liposuction?

Good question! When fat is removed from an area it does not regenerate there. If you gain weight, it will not return to where the fat was removed but build up in other areas. Patients must appreciate this because weight gain can cause significant changes in other areas of the body; back, arms, etc.
Weight gain. After a problem area is corrected with liposuction, weight gain can result in a new "problem" area. For example, if the thighs are suctioned and you gain weight, you may notice the weight gain in your abdomen or buttocks.
Fat after Lipo. If one gains weight after liposuction by not regulating diet and exercise, then fat will be stored in sites other than that which underwent lipo but some fat cells remain in the surgically-treated area and those cells can enlarge as they store more fat than they used to in order to make up for some of the cells that were removed by the liposuction.
Redistribution. It will tend to distribute itself in areas where the fat was not disrupted or removed so if you can a lot of weight, you may end up looking rather disproportionate. The remaining fat cells in the areas liposuctioned also will get larger with weight gain but may be proportionally less than surrounding areas.
Put fat on. You will generally put on fat in areas that were not liposuctioned first followed by fat everywhere as you continue to gain weight when surpassing 15% above your ideal body weight.
Depends: If the patient gains a significant amount of weight, then fat can return to an area previously treated by liposuction. Fat usually does not come back in treated areas *if* the patient does not gain a significant amount of weight after the surgery. With increasing weight the degree of fat accumulation in a previously treated area is proportionately less than in untreated areas.