You assume too much.

I have seen it many times that when Bill leaves, the thing he was responsible for doesn't get picked up by anyone.

It doesn't necessarily even mean that the organization is "abnormal". Perhaps the reason Bill was let go was because X was not considered business-critical any more.

> I have seen it many times that when Bill leaves, the thing he was responsible for doesn't get picked up by anyone.

I LITERALLY offered the "we are probably not going to do that anymore" option. In your situation, you can scratch the probably away. That answer is still actually helpful unlike the original answer.