Is it a lost cause?

Had the dreaded woodpecker raid on our blue tit nest box. Was notified of the first attack by a tap tap tap noise at 7 PM last night, GSW was on the box and had pecked a good-sized hole in the bottom of the box. One chick had either fallen out or "emergency" fledged itself and was flutter-hopping about it allowed me to pick it up and move it to somewhere with a bit more cover aka a bush near the nest box. We have a high cat population around here as well as magpies, so better safe than cat or magpie victim. As of this morning, the parents were still feeding the baby in the bush so all is well there. Woodpecker has been back at the nest box, pecking both sides and base and even the roof. Each time I've chased it off. This has been going on since 4:30 AM this morning. Last attack was about 12 PM and I can see what looks like a little wing on the floor beneath the box and lots of nesting material. Parents have not been back to the box for almost 3 hours now. They're still feeding the baby that's hidden in the bush, and don't seem to be bothered by me sitting nearby as I type this. 

Is it safe to assume that the chicks that were still in the box are now dead or are dying? There have been some flies showing interest so shall assume the former. Is it worth me taking a sneakt peak to make sure so I can clear it out or should I just let nature take its course here and let the flies do their job?