NET

24 For false messiahs and false prophets will appear and perform great signs and wonders to deceive, if possible, even the elect.

Darby

24 For there shall arise false Christs, and false prophets, and shall give great signs and wonders, so as to mislead, if possible^D6914, even the elect.

Darby Bible Notes

possible - 'If possible' gives the purpose of the deceivers; 'if it were possible' would be the judgment of the writer. It seems to me simpler to take it as in text. It still implies 'it is not possible.'

KJV

24 “For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if” [it were] “possible, they shall deceive the very elect.”