This one's throwing me for a bit of a loop. The translation says "He also didn't really take the possibility of anyone being there seriously."
It makes sense to me except for the いはしない part. What does this mean?
I looked up い and saw that it can mean stomach, so my first thought was that いはしない was perhaps some idiom like "not doing his stomach" that means "not being there" but I can't find any evidence to justify that on the internet so I have to assume it's wrong.