Most of the premises of your question are wrong from an Buddhist point of view. You assume death and ego (idea of the self) as true which are considered illusions. See three marks of existence. ref here
Suffering is often produced by attachment to an false idea, desire or not acceptance of existence as it is. One of those features of existence is impermanence (nothing lasts forever). If you attach yourself emotionally to something believing that it will last forever when it doesn't you'll feel devastated. eg. "models who thinks their looks will last all their lives", "actors and actresses who are emotionally dependent on fame because they need other people to admiring them to feed their egos".
How close are we to conquering death? If mind uploading is realized, will it prove the claim that the concept of Death is an illusion?
OK let's suppose you and your loved ones are in computers now as immortal avatars. What if one of those instances are deleted or one server is formatted? Isn't that death too? What if your uploaded wife decided to leave you and have a life on her own? Isn't that break up a form of "death" too? Again this view is produced by a lack of acceptance of impermanence and an emotional attachment. It has to do more with psychology and less with philosophy.
Suppose we were in that mind uploaded word of immortal avatars and they made 5 copies of you. Which one would be you? What if they decided to split up and have a life of their own? After 300 years impermanence they would have changed completely and also would you! What if we are all copies of the same instance with different avatars changed by impermanence through millenea? Then "ego" or idea of the self is also an illusion a creation of the mind and also a creator of endless suffering.
Death is just a form of impermanence which is sometimes good and sometimes bad that needs to be accepted. Is that lack of acceptance that causes most suffering. Mind uploading would be submitted to the same marks of existence as this world (bardo) assuming that we are not in a computer program already.