If the developer exhausts during development time, there will be a curve-shape change; the shoulder will not be as pronounced. It's called compensating development and is a good tool for reining in highlights in very contrasty situations. It maintains film speed, since the shadows get fairly full development. Extending development time to compensate for compensation helps a bit, but I think that the shoulder would still not be as steep and mid-tones would get a bit more separation.
For "normal" scenes, compensation is neither needed nor desired, hence the admonishment to use enough stock/concentrate to ensure that developer activity does not wane during the development time.
In the extreme case, using too little developer will result in the developer exhausting completely before the highlights are "fully" developed. No amount of additional development time will help here.
Best,
Doremus