Yes, it is possible that 1John 2:19 refers to pseudo-Christians, whose profession of faith in Jesus as Lord was insincere or something so that they were never saved and will wind up eternally damned and destroyed.
However, the use of the same verb "remained" in 2:19 and "remains" in 2:24 indicates the possibility
that genuine Christians may/will NOT "see" that the Gospel remains in them so that they will remain in the Son
or continue to be saved.
How can we harmonize these two possibilities?