All of Israel is the 1/3 remnant of Jews who will survive the attacks by the nations
Zechariah 13:8-9, when the Shepherd comes again:
“And it will come about in all the land,” declares the LORD,
“that two parts in it will be cut off and perish; but the third will be left in it. And I will bring the third part through the fire, refine them as silver is refined, and test them as gold is tested. They will call on My name, and I will answer them; I will say; ‘they are My people,’ and they will say, ‘The LORD is my God.’”
Also Zechariah 14 describes God’s Battle with Jerusalem’s Foes (the Nations).
“All of Israel” ... is ... all who are alive then ...
It would be the same today, if I said “all of Israel” in some statement to you right now — I’m definitely not talking about the dead people ... LOL ...
SO ... yes ... ALL of Israel will be saved on the day the Messiah of Israel returns!
Love Zechariah, am going to find it read out loud in Hebrew online.