Inosuke’s boar mask still has the skull inside it. That’s why the eyes in the mask are so big, why it hurts even more to get hit by him and why it still has the tusks.
If you look at any shot of Inosuke’s mask when it falls onto the ground or is held it retains its shape.
Inosuke never really says a whole lot about being raised by the boars and of course being “raised” by an animal isn’t the same as being raised by a human or even a demon, but I’m curious if the squad was able to talk Inosuke into not wearing the mask anymore and using it as a emblem to remember and create a memorial for the boar. Regardless of how long the boar took care of Inosuke before she died, she did provide for his survival and he clearly cared enough about her that he wanted to keep the entire head when he could have just kept a smaller part like just her tusks. But Inosuke is essentially running around wearing his foster mom’s head and if I have to be cursed with that knowledge so do ya’ll!