Wasn't it unconditional?
As I read it, the blessings to Abraham were indeed unconditional and were promised to his seed after him. This included Esau. The blessing was his by right as a descendent of Abraham and as the firstborn of his father Isaac. The blessing was his and known to be his, all through his life, but it seems to me that Esau did not value it.
When he was a little hungry and certainly not near to death he SOLD his birthright for a bowl of hot soup! There was no disobedience involved. He simply thought with his stomach and thought nothing of his birthright.
As the firstborn he had the birth-right of getting the double portion of blessings from his father, but he sold the birthright to his brother. Then when Isaac wanted to bless him anyway (Esau was Isaac's favorite) Jacob supplanted him and took the firstborn blessing for himself. But, Esau was blest that he would live in good land with the dew of heaven. No longer having the birthright blessing of the firstborn, he would be under his brother Jacob in power and strength, though he was promised that after a time he would get his own dominion and not be under Jacob.
Gen 27:38-40 And Esau said to his father, Have you but one blessing, my father? Bless me, me also, my father. And Esau lifted up his voice and wept. And Isaac his father answered and said to him, Behold! Your dwelling shall be of the fatness of the earth and of the dew of heaven from above. And by your sword you shall live, and shall serve your brother. And it shall be when you shall have the dominion, you shall break his yoke from off your neck.
So don't think that Esau lost out because of disobedience. He lost out
because he did not value the gift of God until it was too late!
Best wishes for Grace and the Peace of Jesus.