"If possible" (Gr. ei dynaton, Matthew 24:24) means the false prophets will hope to mislead the elect living in the Tribulation. It does not mean that the elect will inevitably remain true to the faith. Jesus had already said that some of His disciples would abandon the truth under persecution ( Matthew 24:10-11; cf. Matthew 26:31). However the elect will not lose their salvation. [source][source][source]