Ego = Evil Inclination
In Judaism, what you’re calling the ‘ego’ or sense of ‘I’ is often referred to as a person’s evil inclination.
Humans are unique, inasmuch as we’re part animal (ie, the body) and part Divine (ie, the soul). Our emotions and intellect are the connecting material between these two parts, and is considered to be the third part of the human soul.
The struggle of humanity is to raise their intellect and emotions ‘upwards’, towards spirituality, instead of having them get pulled ‘downwards’ towards materialism and our coarsest desires. (But to say this is not easy is the understatement of the century. Even the worst evil-doers intellectually justify the terrible things they do, and come up with ‘logical’ reasons why they have to act the way they act.)
Each of us has in inclination to do ‘evil’ (defined as going against what God wants, however God Himself chooses to define that) and to do ‘good’ (defined as doing what God wants, again however God Himself chooses to define ‘good’).
The soul is always and only 'good'
The ego or I (what I’m calling the evil inclination) is rooted in a person’s body, and manifests itself in all our lusts, negative character traits, bad habits and nasty behaviours.
The intellect and our feelings are ‘neutral’ are can be pulled in either direction (which is why the real struggle between good and bad takes place in our mind and our emotional state) and our soul is only and always good.
Now with that background out the way, I can try to answer your question.
Great idea, but impossible to achieve
In theory, the idea of ‘ego death’ or killing off your evil inclination is great, and the ultimate goal of all humanity. In practice, it can never be achieved 100%. Why not? Because as a person progresses up the spiritual ladder, the struggles they have with their evil inclination get bigger, in order to maintain their free choice.
At the beginning of the process, it’ll be bog-standard stuff like getting out of bed on time, quitting cigarettes and holding more doors open for people. But as you go higher up, the struggle moves out of ‘bodily lusts’ and into ‘ego gratification’ – and that’s a much harder battle to win, because most of the time you’re not even aware of your true motivations.
Sometimes, as people build images of themselves as ‘holy’, good and ‘ego-less’ individuals, they start performing their devotions and acts for the kudos, acclaim, power and prestige they’ll get from other people.
Feivel the holy egotist
There’s an apocryphal Jewish parable from the time of the Baal Shem Tov, a famous Jewish Rebbe and mystic who lived around 350 years’ ago, in the Ukraine, that illustrates this point nicely. It goes like this:
‘There was once a man called Feivel, who developed a reputation in his local Jewish community for being a truly saintly individual, because he would fast from one Sabbath to the next (ie, 6 days straight). Feivel would sit outside his home as the holy Sabbath began, and as the townsfolk made their way to the local synagogue to pray, they’d all nod in his direction, or come over and praise him for his tremendous holiness and piety.
‘One week, the BESHT heard Feivel being highly praised for his enormous saintliness and shook his head sadly. When someone asked what was wrong, he replied: “Let the townspeople go to synagogue next week by a different route.” This was done, and the alternative route to the Synagogue didn’t go past Feivel’s front door. That Sabbath, Feivel died.
“When the townspeople came to the BESHT asking for an explanation, he sadly explained that Feivel’s fasting had not been for the sake of Heaven, but for all the honour and acclaim he was getting from his neighbours.”
To sum it up, when Feivel didn’t get patted on the back by his comrades for being so pious and self-effacing, his ego took affront and he died on the spot.
So to sum it up:
What you’re calling ego-death is in theory a good thing. The spiritual goal of humanity is to do their best to devote their life to doing what God defines as ‘good’, even when that goes against their own basest desires.
In practice, it’s impossible to achieve this all of the time. A few people (literally a handful in the whole of humanity) are capable of coming close to it, but the battle against the ego, (what Judaism calls the ‘evil inclination’) continues right up until the last moment of death.
Many other people strive to achieve this sort of spiritual enlightenment, some for good motives, others for the power, prestige, ego-boost and kudos that being such a ‘holy’ person will give them (if only as an internal comparison, ie, ‘I’m so much better than so-and-so because I do x, or don’t do y’).
Ironically, no-one who’s genuinely come close to achieving true spiritual enlightenment – what I’m defining as nullifying themselves completely to God’s will, as defined by God Himself - would ever claim to others that they’ve done so, as that’s the ultimate boast.
So if someone is claiming they’ve achieved ego-death, they’re either out for kudos or they’re out of touch with reality (which would suggest some form of being ‘bonkers’, however mild). And if they have really achieved it, then no-one else would ever really know that, which would suggest they truly have achieved a very high spiritual level.