If the cat got in through a cat flap then it will be able to get out. Assuming obv that the flap isn’t locked from the outside
Reality is that cats have survived locked up in sheds and garages and such for days and while they might have been a bit thinner haven’t come to extreme harm.
A cat isn’t going to starve to death in 48 hours.
Presumably if they’re having work done whoever is doing the work will be back tomorrow. The cat will be fine in there until then.
You absolutely cannot break into the house. The RSPCA wouldn’t even come out to my cat who was still a 9 month old kitten who climbed up on to the roof of a house for at least 72 hours. And there’s no way the police or fire brigade should be expected to break into someone’s house to rescue a cat.
He’ll be fine until tomorrow.