Isekais nowadays rarely have the MC go back to their world and deal with the consequences of their disappearance. So this is refreshing to see, even if it's for more drama.
His mom was probably wondering why her son went radio silent and wouldn't talk to her. Since he got sent to the other world, it's not like they could find a body.
And from what the neighbor said, it looks like she never gave up hope on Ellison. Handing out missing flyers would be her accepting that her son has disappeared, so she didn't do that.
This is too much, I feel so bad for the mc, his mother must have loved him so much that the son would want to meet her despite willing to go back to the world. This is just too sad for the mc