No salvation possible then for those left behind?
Of course not. Once Jesus comes it will be too later for anyone to repent and be saved. Today (now) is the day of salvation (2 Cor 6:2)! People need to repent now before it's too late and it will definitely be too late once Jesus comes.
Have you never read this:
Luke 17:26 And as it was in the days of Noe, so shall it be also in the days of the Son of man. 27 They did eat, they drank, they married wives, they were given in marriage, until
the day that Noah entered into the ark, and the flood came, and destroyed them all. 28 Likewise also as it was in the days of Lot; they did eat, they drank, they bought, they sold, they planted, they builded; 29 But
the same day that Lot went out of Sodom it rained fire and brimstone from heaven, and destroyed them all. 30 Even thus shall it be in the day when the Son of man is revealed. 31 In that day, he which shall be upon the housetop, and his stuff in the house, let him not come down to take it away: and he that is in the field, let him likewise not return back. 32
Remember Lot's wife. 33 Whosoever shall seek to save his life shall lose it; and whosoever shall lose his life shall preserve it. 34 I tell you, in that night there shall be two men in one bed; the one shall be taken, and
the other shall be left. 35 Two women shall be grinding together; the one shall be taken,
and the other left. 36 Two men shall be in the field; the one shall be taken,
and the other left. 37 And they answered and said unto him, Where, Lord? And he said unto them,
Wheresoever the body is, thither will the eagles be gathered together.
Throughout this passage Jesus indicates what will happen to believers when Jesus comes and the rapture occurs and what will happen to unbelievers at that time. He compares what will happen on the day He returns to what happened on the day Noah entered the ark which was that the flood came and destroyed all unbelievers (everyone left behind apart from the safety of the ark). He also compared what will happen on the day of His second coming and the rapture to what happened on the day Lot went out of Sodom. Those left behind in Sodom were all killed by the fire and brimstone that came down from heaven. Jesus said "Even thus shall it be in the day when the Son of man is revealed.".
Does that seem to you that Jesus was saying anyone left behind could be saved when He purposely pointed out how no one left behind off the ark and no one left behind in Sodom were saved and compared that directly to the day of His second coming?
Then look at what He said after that. He said to remember Lot's wife. What did Lot's wife do? She looked back at the city despite being told not to do so. She cared more about her temporary life in this world than about eternal life with God, so she paid the price for that. She missed her life in the evil city of Sodom and that showed where her heart truly was rather than being submitted to God and His will instead. Anyone who is like that when Jesus returns will perish, also. And anyone left behind on the earth instead of being caught up to meet Christ in the air will be killed just as everyone left outside the ark was killed in Noah's day and everyone left in Sodom was killed in Lot's day. That's why Jesus talked about one being taken and one left behind. There's two possible things that will happen to all people on the day Christ returns. Everyone will either be changed to have immortal bodies and be caught up to meet Christ or they will be left behind and killed and will become food for the eagles or vultures, which is what verse 37 is about.