The tragic irony of this speech is identified when Linda closes this speech, and the play, with the final words that she utters. Note what it is precisely that she says as she addresses her husband's grave and the stage directions that accompany it:
I made the last payment on the house today. Today, dear. And there'll be nobody home. A sob rises in her throat. We're free and clear. Sobbing more fully, released: We're free.
After working for so many years in a job that he was never suited for, Willy has finally paid of his mortgage. The irony is that now that he and Linda are free from their financial debt and obligations, he is now no longer able to experience and enjoy that freedom with Linda. It is immensely tragic that at the time when Willy and Linda should be happy, Willy chooses to kill himself. I wonder too whether there is a note of irony when the stage directions refer to Linday being "released." Is there a sense in which Linda is really talking about how she is free and doesn't have to worry about her delusional husband any more? What do you think? Either way, the chief irony is the way in which they now should be settling down and enjoying retirement without any financial burdens. However, Willy's suicide has left Linda to enjoy this by herself.
What kind of irony is that?
I disagree. it's not irony,
I think it's verbal irony