This is a pretty offensive question, but I'm assuming it was written by someone who doesn't particularly love his/her parents the way most people love theirs.
When you love your parents the way children usually love their parents, you aren't thinking about what you get from them. You're thinking about what you can give to them or do for them - because that's what real love is all about. For people who love parents the way most love their own, there's no way they can even allow themselves to think in terms of their parents' stuff and of them dying, because it's just unthinkable.
So, if a son or daughter doesn't love their parents the way most people love their own, it might suggest that there will be no inheritance because the relationship between the parents and their child is not a good one. I had an elderly friend who knew her kids and grandchildren were "waiting" for their "inheritance", so she donated a bunch of her money to things like animal causes and made sure nobody but two very close and caring family members got any of her money.
There is no "should" when it comes to whether someone eventually inherits anything from his parents or anyone else.
I'd suggest grown children get their minds of what is not theirs and what they aren't necessarily entitled to and, instead, figure a way to earn their own money and belongings. This is good advice because the world is full of parents who make good and sure their kids don't inherit anything at all.