Not only in the next life, but in this very life these mundane insights
are "lost" as soon as one loses concentration or stops meditating. Though
one may clearly discern anicca, dukkha, and anatta while meditating, when
one stops meditating, perceptions of permanance (nicca), pleasure (sukha), =
and self (atta) soon reassert themselves.
However, gaining the mundane insight knowledges is like sowing valuable
seeds of wisdom that can sprout and give fruit in the future. If one has
not gained such seeds of insight in this life, even if one meets the
future Buddha Metteyya, one will not be inclined to meditate and put an
end to suffering. If one has such seeds of insight, the inclination or
potential is there, and will bear fruit when conditions are ripe, perhaps
on one's deathbed one may gain nibbāna.
Supramundane seeds of magga and phala ñāna are so fertile that they wi=
invariably bear fruit, but even a Stream-winner may be somewhat negligent
and fail to attain the higher paths in this very life.
As it says in the Dhammapada:
Do not disregard merit, saying "It will not come to me";
by the falling of drops even a water-jar is filled;
likewise the wise man, gathering little by little,
fills himself with good. (Dhp v 122)