Based on what the characters say, Biff will attempt to find a job and maintain it. He has realized that his ambitions and self-image were false and outstripped his actual talents, abilities, and even his interests. He has achieved a new humility and plans to act upon it to create a life based on reality, not dreams.
Happy, on the other hand, dedicates himself to pursuing Willy's dream. He speaks at Willy's funeral to this end, stating that Willy's dream is the only dream a person can have. Happy aligns himself with Willy, in his flaws, his goals, and his delusions.
We can predict that he will fail to achieve his dream as he is ill-equipped like Willy was to pursue the adventure and success that uncle Ben achieved.
In the end, Biff followed his heart and having decided to follow his dream, he probably went to look for an outdoor job, may be on a farm. But he kept in close touch with his mother Linda because they got really close just about the time Willy killed himself.
Happy, being one character that never "grew" followed his father's footsteps probably chasing dreams which would be vain and wouldn’t make him achieve happiness.
Linda was most probably left alone in the house miserable, sad and still confused as to why Willy killed himself.
The likelihood of the insurance company discovering that Willy's accident was intentional is high given that Linda had hinted the insurance company had evidence of Willy attempting to crash his car before as witnessed by a woman. So, the family may not have gotten the insurance money, hence, no business establishment by Biff and Happy. So Willy's death would have been vain and "non-beneficial" to his family.