Final answer:
Not being rescued by the plane would significantly impact Brian's mental state and likely lead to increased self-reliance and maturity, as well as a deeper connection with the natural world.
Step-by-step explanation:
If Brian is not rescued by the plane that flew over, the effect on him would likely involve a deepening sense of isolation and despair, as well as an intensified need for self-reliance.
His disappointment at not being seen may lead him to further hone his survival skills and become more in-tune with his environment, triggering a growth in his independence and resourcefulness.
The psychological impact of such an event could potentially be profound, further developing his character and his ability to adapt to challenging situations.