Cut off

Means to kill, die or come to an end.

For example: Genesis 9:11, 1 Samuel 24:21, 1 Kings 18:4, Isaiah 53:8

From heaven

To say that someone or something "come from heaven/God" is a Jewish idiom that means he or it is good, for example:

There was a man sent from God, whose name was John. -- John 1:6

and

But Jesus answered and said to them, “I also will ask you one thing, which if you tell Me, I likewise will tell you by what authority I do these things: The baptism of John — where was it from? From heaven or from men?”

And they reasoned among themselves, saying, “If we say, ‘From heaven,’ He will say to us, ‘Why then did you not believe him?’ But if we say, ‘From men,’ we fear the multitude, for all count John as a prophet.” -- Matthew 21:25

Nobody believed John was coming from heaven. The issue was that "from heaven" means "it is good" and therefore they were supposed to accept John's baptism and "from men" means "it is bad" which would have offended the people.

Another example:

Every good gift and every perfect gift is from above, and comes down from the Father of lights, with whom there is no variation or shadow of turning. -- James 1:17 (NKJV)

and

"And try Me now in this," says the LORD of hosts, "If I will not open for you the windows of heaven and pour out for you such blessing that there will not be room enough to receive it." -- Malachi 3:10 (NKJV)

Nobody expected "good gifts" or "blessings" to literally fall out of the sky.

With this in context, John 3:31 also makes more sense if it is interpreted as an idiom:

He who comes from above is above all; he who is of the earth is earthly and speaks of the earth. He who comes from heaven is above all. -- John 3:31 (NKJV)

It should not be taken literally, then John would have meant that Jesus' disciples were also previously in heaven or some other place other than our world

As You sent Me into the world, I also have sent them into the world. -- John 17:18 (NKJV)

Jesus' disciples were already on Earth. As a literal interpretation Jesus' statement does not make sense, but in the context of this idiom it means they will continue the "good work" that God originally sent Jesus to do.