  Recent studies suggest that cold dark matter subhalos are hard to disrupt and
almost all cases of subhalo disruption observed in numerical simulations are
due to numerical effects. However, these findings primarily relied on idealized
numerical experiments, which do not fully capture the realistic conditions of
subhalo evolution within a hierarchical cosmological context. Based on the
Aquarius simulations, we identify clear segregation in the population of
surviving and disrupted subhalos, which corresponds to two distinct acquisition
channels of subhalos. We find that all of the first-order subhalos accreted
after redshift 2 survive to the present time without suffering from artificial
disruption. On the other hand, most of the disrupted subhalos are sub-subhalos
accreted at high redshift. Unlike the first-order subhalos, sub-subhalos
experience pre-processing and many of them are accreted through major mergers
at high redshift, resulting in very high mass loss rates. We confirm these high
mass loss rates are physical through both numerical experiments and
semi-analytical modeling, thus supporting a physical origin for their rapid
disappearance in the simulation. Even though we cannot verify whether these
subhalos have fully disrupted or not, their extreme mass loss rates dictate
that they can at most contribute a negligible fraction to the very low mass end
of the subhalo mass function. We thus conclude that current state-of-the-art
cosmological simulations have reliably resolved the subhalo population.
