Since this is all conjecture, there really is no wrong answer, so here goes :-)
Becuase they really haven't been paying attention, the insurance company doesn't figure out that Willy committed suicide, and so Linda eventually gets the $10,000. She keeps $2000 and gives Happy $4000 and Biff $4000. Predicably, the money doesn't make a very big difference in the Lomans' lives.
Happy said of his father at the funeral:
He had a good dream. It’s the only dream you can have — to come out number-one man. He fought it out here, and this is where I’m gonna win it for him.
What his father went through has taught him absolutely nothing, and so he will continue to be a disappointed businessman, a braggart, and a lowly womanizer. Eventually he will marry someone in his office, treat her badly, cheat on her, get divorced and spend the rest of his life drinking and dreaming of the life he could have had.
Biff takes the money and moves back to Texas. He buys a little ranch, marries a woman who is a lot like his mother, unpretentious and gritty. They have have two little girls and live happily ever after.
With Biff in Texas and Happy all into himself, Linda is alone for a while. One day, her kitchen sink develops a leak. She goes next door to see if Charlie knows the name of a good plumber. Well, one thing leads to another, and eventually Charlie and Linda get married, and they, too, for the few years they have left, live a comfortable and satisfying life together.