Son in law

Some people don’t like fuss. Maybe he’s an introvert. Just leave him alone and go without him.

My son dislikes big family gatherings,it's just the way he is,my DIL always tells him when things are going to happen and her family know that he probably won't attend,I'm sure your daughter knows this ,just go and leave him to it

I wouldn’t think his absence should spoil your day, why rearrange it? Unless his mother was doing something with you for Mother’s Day and both sides were in attendance. Or does your daughter have to stay with him when he is unwell??
Sounds as if you need to stop arranging things with his attendance being pivotal if he is a bit of a wet lettuce, every family has one, just plan without him needing to be there next time.

Leave him where he is and go and have some fun. If I had waited for the men in my life to organise or contribute to any celebrations my life would be a complete misery by now.

How upsetting for you and your family. Does he fall "ill" often or does he use other excuses? Is he generally anti-social or does he like the attention to be on him and his health most of the time?

Can’t you all go and leave him in bed ‘recovering’