From a metaphysical perspective, we could argue that the key to this answer is in the words spoken by Linda:
We are free. We are free.
This is because the entire Loman family was, during Willy's life, in fact, trapped inside the mind and mentality of Willy Loman. Although Biff, Happy, and Linda (as individuals) are responsible for their own actions, the fact is that is that they had very little control of their lives..because of Willy!
His deep and insistent influence in their ways of thinking, and acting, is what makes Linda co-dependent to him, and what makes Happy and Biff clueless in life.
Notice how, first, Willy creates an image of himself as a big-shot salesperson who is well-liked, and admired everywhere. Although this is merely his hope, and not his reality, Willy believes that, by thinking that it has already happened, it will become real.
He then instills this same pattern of thinking in Biff who, in his own words, admits that Willy has "blown him up with hot air". Living vicariously through Biff's own efforts to please a supposedly-bigger-than-life father, Biff and Willy feed each other's fantasies interdependently. This is what leaves Biff, literally, in limbo once he finds out that his father is, as he calls him, a "fake".
Happy is never part of the dynamics between Willy and Biff, for he is made to worship and follow Biff around. As adults, where the roles have changed and Biff is no longer a high school hero, Happy still seeks for Biff's grandiosity, and gladly accepts the fantasies of the family, as long as he can stay drama-free. He, however, is also a fake who lies consistently trying to make himself bigger than what he really is.
Linda has been wrapped within Willy's mind frame forever. She is Willy's enabler, his wife, nurse, nurturer, everything. She is so caught up in Willy's web of lies that she believes them to the point of asking Willy to decline Ben's offer to go to Alaska "because he has a beautiful job" already. Linda uses denial to be able to make it "day by day" like she says. However, she is clearly in a constant battle, walking on eggshells and looking after Willy like you would look after a mental patient.
Hence, the positive of it all is that now that Willy is gone, the family's spell of deception and lies will finally be lifted. They will perhaps have to find themselves again, but they will nevertheless be able to do it freely. One, single, person can ruin an entire generation. This is what Willy was doing, without his knowledge. However, the family is now free from him and his influence.