Good question, but I'm don't think that his suicide is symptomatic of the way he has lived. But it does represent his continuing belief in the American dream.
Willy and his brother Ben represent two ways of being successful. Willy chose to work hard in one organization. He puts in thirty-five years, expecting to be rewardid with a good salary and the respect of his colleagues. Ben is the opportunist. He makes quick money. He comes out of the jungle a rich man. In many ways, Willy wants Biff to follow Ben's example. All Biff needs is a stake, and he can make it big. This is why he presses Biff to go to his former boss to help set him up in the Loman brothers sporting goods enterprise.
Willy himself always regretted not going with Ben to Alaska when he had the opportunity. In his final scene, Willy imagines that he is talking with Ben. He sees his suicide as a business deal, a proposition, that will have an excellent return: "twenty thousand dollars on the barrelhead." With this insurance money, Biff, Willy believes, will make it big.
Willy's suicide is a gamble, a proposition, an enterprise, much like Ben's venture in the diamond mines. And the venture he did not take to Alaska. It does not represent the way he had lived, but the way he wished he had lived.
I agree with most of the previous answers, however, you can always change perspectives and see the way it is symptomatic as an impulsive reaction--which is how Willy always reacted--to life.
It may be symptomatic if we analyze it from the perspective that Willy has never once stopped to think about any consequences to his actions: He is a salesman, a man on the go. There is no rest for the wicked. He himself goes by the dream of achieving, succeeding, attaining, being larger than life, and being liked. He accomplished none of these things because of his impulsive nature, his arrogance, and his poor social skills.
Therefore, this same impulse that forbade him from making sensible choices was topped by the ultimate impulsive act: Suicide.
In the play by Arthur Miller Death of a Salesman Willy Lowman wears the name that corresponds to his last position in life. He is the low man in a company where once he was a mediocre salesman, but where he has raised his own beliefs to think he had been a very good salesman.
Willy has spent his life struggling to attain the American Dream; his own home with a clear mortgage, a family, and a comfortable life. He finds himself on the cusp of losing his home, having to borrow money from the company owner and failing at sales.
For Willy, his death is all he has left. He knows that he is worth moe dead than alive and he kills himself to obtain the insurance money for his family. His life has been a series of unfortunate events and so is his death.