What is the best case scenario for scar removal by plastics guy?

Improval. Scars can often be improved or made less visible with scar revision surgery but cannot be removed. Scar treatments can include laser or sanding (dermabrasion) or perhaps surgical revision. Surgery is usually done to reduce the overall amount of scar or to reshape or reposition a scar. There is no way to completely remove a scar however.
Thin fine line. The best possible scar is flat, thin, and evenly colored to match your normal skin. If you have a scar that is wide, raised, or discolored, your plastic surgeon should be able to offer you some imporvement in each of these areas with revision surgery, injections, gel treatments, massage, or some combination of all of these.
Fine concealed scar. Our goal is to minimize or improve scars; removal is virtually impossible. For example we can convert a vertical lower belly scar into a horizontal one that can be concealed beneath a bathing suit. Other scars can be made less thick, less raised, less red, less deep, less pigmented, etc. Sometimes a scar can be softened but it is usually with a less visible scar.
Improved appearance. Usually scar reduction and redirection can improve the appearance of scarring. By following natural lines, smaller scaring is result. Careful suturing under the skin helps prevent spreading and poor scar appearance. Often after reduction, use of surface treatments like abrasion, laser remodeling, etc can help with the surface texture.