Blue tit nesting box fallen

We have a blue tit nesting box that went up a number of years ago but was never used and has been finally used this year. Unfortunately, this morning the attachment failed and the box fell and although I think I managed to put it back up almost immediately, (and much more securely!) a blue tit definitely saw me holding it and putting it back. I think that it is reasonably undamaged although I didn't look inside. 

Is there hope for the nest inside and is there anything that I can do to help it or the blue tits? I am almost certain that there weren't any chicks yet.