I wonder if the OP is ever going to come back and update us? I really hope her cat has turned up - indoor cats often freak out at being outside because they haven't been allowed to get used to it gradually. It's probably hiding out somewhere very close.
I'm finding this thread very comforting with all the Returned Cats stories, as mine has gone missing for the second time this summer. Back in May/June, he started spending longer and longer away from home, pulling the occasional all-nighter and not returning until late the next day, and I had a feeling he was going to string his adventures together. And he did - he disappeared for 5 long days and nights and we were distraught. We did EVERYTHING that's always recommended, but in the end found him accidentally, while out leafletting a hamlet the other side of a vast field! By day 5 I think he was ready to come home and allowed us to pick him up and take him back. When we were ready to let him out again we put him in a GPS tracking collar and were horrified to see the extent of his range! And yes, he's neutered, though I often wonder if the vet missed one of them. He hadn't even lost much weight - he's an excellent hunter and was presumably living off voles, and maybe the odd sheep.
This time he's been gone less than 48 hours, but it's much colder at night and I'm worried about the feral little sod. This morning I went out just after dawn, and was out late last night, and four times yesterday. Now we know his range, at least we know better where to look.
Sadly, I suspect he's just not that into us (unlike his brother, who lives for his stomach and comes back to the house several times an hour, and also because of his deep affection for us) and he has a wild little soul. I imagine him grimly telling himself 'Nothing tastes as good as freedom feels' whenever he has a wobble out there.