Fledgling day

Hi everyone, first year of putting up a nestbox for a blue tit family. I have watched others previously over last couple of years so understand some of tbe behaviours. 2 fledged this morning Nd within couple of hours they were up onto the tree and flying about. There is obviously at least one more in the nest box chriping away but i have seen parents fo while, i know sometimes there can be a day between fledglings but is there ever a case not to return for them at all?