While the advice to lie to him about her death makes sense at first,
however, from the lens
of deeper wisdom, understanding the fact that we are not just a body
with flesh and bones, but also a Spirit with a Soul that never die, you can answer truthfully that she's ALWAYS around,
but just not there physically.
And if you are able to connect with him at the Soul level, he will not argue this. There's something almost magical and divine that takes place there!