Will there still be people alive when Jesus returns?

You say:

I have heard many people, including some pastors say that “we all are going to die” But where is it written in the bible that states everyone on earth is going to die before Jesus returns? Will there still be people alive upon his return?

Yes there will be people alive when Jesus returns.  The Bible does not state that everyone on earth is going to die before Jesus returns.  In fact, the Bible clearly says or implies in many places, that there will be people alive at Jesus return.  Consider the following passages:

Speaking of the battle just prior to the return of Jesus:

Zechariah 14:16  Then everyone who survives of all the nations that have come against Jerusalem shall go up year after year to worship the King, the LORD of hosts, and to keep the Feast of Booths.

So we see there will be survivors from this battle — survivors who will convert and worship the LORD of hosts.

Jesus’ well known parable of the ten virgins:

Matthew  25:1-13  “Then the kingdom of heaven will be like ten virgins who took their lamps and went to meet the bridegroom.  (2)  Five of them were foolish, and five were wise.  (3)  For when the foolish took their lamps, they took no oil with them,  (4)  but the wise took flasks of oil with their lamps.  (5)  As the bridegroom was delayed, they all became drowsy and slept.  (6)  But at midnight there was a cry, ‘Here is the bridegroom! Come out to meet him.’  (7)  Then all those virgins rose and trimmed their lamps.  (8)  And the foolish said to the wise, ‘Give us some of your oil, for our lamps are going out.’  (9)  But the wise answered, saying, ‘Since there will not be enough for us and for you, go rather to the dealers and buy for yourselves.’  (10)  And while they were going to buy, the bridegroom came, and those who were ready went in with him to the marriage feast, and the door was shut.  (11)  Afterward the other virgins came also, saying, ‘Lord, lord, open to us.’  (12)  But he answered, ‘Truly, I say to you, I do not know you.’  (13)  Watch therefore, for you know neither the day nor the hour.

This parable indicates there will be believers alive at Jesus’ return — some are vigilant, some are not.

Jesus spoke at length about conditions before his return in Matthew 24, Mark 13 & Luke 17 & 21.  These verses from Matthew 24, show that some will be taken and some will be left — these people are going about their normal activities when Jesus returns:

Matthew  24:36-47 (LITV)  But as to that day and that hour, no one knows, neither the angels of Heaven, except My Father only.  (37)  But as the days of Noah, so also will be the coming of the Son of Man.  (38)  For as they were in the days before the flood: eating, and drinking, marrying, and giving in marriage, until the day when Noah went into the ark.  (39)  And they did not know until the flood came and took all away. So also will be the coming of the Son of Man.  (40)  At that time two will be out in the field; the one is taken away, and the one is left;  (41)  two grinding at the mill; one is taken away, and one is left.  (42)  Watch, then, for you do not know in what hour your Lord comes.  (43)  But know this, that if the housemaster had known in what watch the thief comes, he would have watched and not have allowed his house to be dug through.  (44)  Because of this, you also be ready, for in that hour you think not, the Son of Man comes.  (45)  Who then is the faithful and wise servant whom his Lord has set over His household, to give to them the food in season?  (46)  Blessed is that servant whom his Lord shall find so doing when He comes.  (47)  Truly I say to you, He will set him over all His substance.

The apostle Paul makes reference to the return of Jesus and the resurrection in his first letter to the Thessalonians:

1 Thessalonians  4:14-17  For since we believe that Jesus died and rose again, even so, through Jesus, God will bring with him those who have fallen asleep.  (15)  For this we declare to you by a word from the Lord, that we who are alive, who are left until the coming of the Lord, will not precede those who have fallen asleep.  (16)  For the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. And the dead in Christ will rise first.  (17)  Then we who are alive, who are left, will be caught up together with them in the clouds to meet the Lord in the air, and so we will always be with the Lord.

Here we see that the dead in Christ will be resurrected first, then the living saints will be caught up with those resurrected and meet Jesus as he comes.

The last passage I’ll mention is from Paul’s first letter to the Corinthians:

1 Co 15:51-54  Behold! I tell you a mystery. We shall not all sleep, but we shall all be changed,  (52)  in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised imperishable, and we shall be changed.  (53)  For this perishable body must put on the imperishable, and this mortal body must put on immortality.  (54)  When the perishable puts on the imperishable, and the mortal puts on immortality, then shall come to pass the saying that is written: “Death is swallowed up in victory.”

Verse 51 plainly states that we shall not all sleep.  “Sleep” is the New Testament way of describing the death of the saints.