Is my cat voting with his feet?

[happygardening]

We've owned this cat for 7 years he's very handsome but not exactly Mr Friendly or Mr Adventurous! He just about tolerates lives with two dogs and a younger cat. He has a dog free area, the whole top two floors of my house, he's fed up there, has a litter tray and his thrown chair.
Up until three weeks ago he was a fair weather cat, in the winter he eats, sleeps, pees, poos, in the spring and summer he goes out for a few hours, in very hot weather he has been out all night. When he doesn't get his own way i.e. not fed when he thinks he should be, the other cat is on his chair, we have visitors to stay doesn't like the food or my DS's comes home from school/university he pees all over our beds it's cost me a fortune having the duvets repeatedly washed!
But recently he's started to go out for long periods even in the rain, I call him but he doesn't come in, today he was gone for over 24 hours, he just come back meowing but not hungry.
I think he's found a new home. Frankly it's fine by me he can pee on their beds but I just worry when he doesn't come back that he's lying ill somewhere.
A friend suggested putting a collar on him with a message something like "please call me if you looking after my cat, I'm not cross but I'd just like to know he's ok". What to you think?

[Fluffycloudland77]

I'd do collar with a note. If they want him they can transfer chip details etc.