NO SIGN OF HIM= I can't find him anywhere.

COME TO DIE= (come-came-come) Here, the verb COME is in the past participle (=he has come to die)

AVADA KEDAVRA= /əvɑ:də kədɑ:vrə/ A magical spell to make incantations. In Harry Potter stories, it is the worst magic spell, causing instant death. In modern English (and many other languages) we still use the word abracadabra /æbrəkədæbrə/ as a magical spell for anything (almost childish now). But originally it was an incantation to heal. The first known mention of the word abracadabra was in the 2nd century AD in a poem called De Medicina Praecepta by Serenus Sammonicus, physician to the Roman emperor Caracalla, who prescribed that malaria sufferers wear an amulet containing the word written in the form of a triangle. But that Latin word came from the Aramaic avada kedavra, and it literally  means 'let the thing be destroyed' (the thing = the illness). Rowlling (the author of the story) changed the sense of the spell to make that "thing" be the person in front of you. That deathly meaning may have come as an inspiration from the Latin word "cadaver" /kədɑ:və*/ (= corpse), also used in medical English jargon.

WORTH= (adj.) /wɜ:*θ/ Deserving or meriting.
This adjective is followed by –ING, so if it is good enough to live for, it is "worth living for".
- That movie is really worth watching.
- Oh, I won't go there, it's not worth the trouble.
- If something is worth doing, it is worth doing it right (English proverb)
- If it's worth having, it's worth fighting for.

DEATHLY= Related to a dead person or characteristically of a dead person in some way (don't confuse with DEADLY = Fatal, causing death). A "deadly house" is a house where you will find death, but a "deathly house" is a house that looks gloomy and scary, ghostly, like the house of dead people.

HALLOWS= The title "The Deathly Hallows" sounds really enigmatic for modern people, especially if they speak American English and are not too familiar with old traditions.
The word "hallow" in modern English is used as a verb and means "to sanctify, to consecrate", as in the Lord's prayer (Our Father who art in heaven, hallowed be thy name, thy kingdom come, thy will be done...). But in this strange title, "the deathly hallows", this word is used as a noun, which may sound shocking. This is because the word is used with a very old meaning which often appears in British Celtic legends. Some important and powerful objects in legends could be referred to as "hallows" because of their function and symbolism. Coronation ceremonies for monarchs still invokes four ritual objects, now represented as the sceptre, sword, ampulla of oil, and crown, and those objects could also be considered "hallows". In Harry Potter, the Deathly Hallows refer to three legendary magical objects (supposedly obtained from Death himself) mentioned in a fairy tale: the Elder Wand, which could defeat all others in battle, the Resurrection Stone, which could bring back the souls of the deceased, and the Cloak of Invisibility, which could hide the wearer from most forms of detection and shield them from many magic spells. Together the objects were said to make their owner a "Master of Death". These objects are called "deathly" because they were in possession of dead people, and now Harry must find them before You-Know-Who does.

Out of curiosity: In old English, the word "hallow" (from Germanic) means "saint" (from Latin), related to the modern adjective "holy". The "All Hallows' Day" is a Catholic celebration which literally means "All Saints' Day", and the day before is the celebration of the dead, so it is called "All Hallows' Even" = modern "All Hallows' Eve" (the day before "All Saints Day") and which led to the modern word "Halloween", which is today, in Anglo-Saxon countries, a day of scary monsters because that night all the spirits of the dead could be wandering the earth.