Could you define what you mean by "working?"
Consider the first word is affordable, is that working?
My assistant has a special needs child.
In a few years, the child will be over 18.
At that time, without the ACA, my assistant would have to purchase insurance out of her pocket.
Now, with the ACA, my assistant can keep the child on the company healthcare plan.
This will save her thousands of dollars per year.
???
If the company has a health insurance plan and your assistant is on that and her s/n child is covered, he can still be covered even if he's over 18.
The more likely scenario is that if you have a company health insurance plan today, due to the (un)aca the company may choose to get rid of that plan and everyone at your company will have to go find insurance elsewhere, including the woman and her child.
We just finished Open Enrollment. Sorry to burst your bubble.