Praise be to Allah, and may peace and blessings be upon the Messenger of Allah.
We do not know of any authentic, explicit text explaining whether some of those who embraced Islam during the time of Jesus, peace be upon him, will apostatize after his death. Therefore, it is not correct to state with certainty that this will or will not happen, because this is one of the matters of the unseen, and we speak about such matters only on the basis of evidence.
In principle, it is not unlikely that some people might outwardly profess Islam during the time of Jesus, peace be upon him, out of hypocrisy, just as happened during the time of the Prophet ﷺ. This was despite that being the best of generations and despite revelation being sent down. There were hypocrites among the people who outwardly professed Islam while concealing disbelief.
However, what is authentically established in the Sunnah is that faith will not remain on earth until the Hour is established. Rather, Allah will take the souls of the believers before it occurs, and the Hour will not be established except upon the worst of people.
The Prophet ﷺ said:
“The Hour will not be established until it is no longer said on earth: Allah, Allah.” Narrated by Muslim.
It is also authentically reported in the hadith of Abdullah ibn Amr, may Allah be pleased with them both, that Jesus, peace be upon him, will kill the Antichrist (the Dajjal). Then people will remain for a period during which security will prevail. Afterwards, Allah will send a cold wind that will take the soul of everyone who has even the weight of a speck of faith in their heart. The worst of people will then remain; they will worship idols, and then the Hour will be established upon them.
Therefore, what is certain is that faith will disappear from the earth before the Hour is established, and the souls of the believers will be taken first. As for whether a specific apostasy will occur among some of those who accepted Islam during the time of Jesus, peace be upon him, after his death, we do not know of any text establishing this. Therefore, one should not speculate or make a definitive claim about it.
And Allah knows best.