What is the difference between "would have been" and "will have been"?
Answer:
The difference is between certainty that something will happen vs. certainty that something will not happen because of some condition in the future.
"Will have been" is used when talking about events such as birthdays, anniversaries, etc., that will occur at a future date. Example: "My husband will have been working for XYZ company 30 years next January 30th."
"Would have been" is used when talking about events such as birthdays, anniversaries, etc., that will not occur at a future date. Example: "If my husband had not passed away last year, he would have been working for XYZ company 30 years next January 30th."