Fledglings disappear all the time, it doesn't mean they are in trouble. Remember there was a chick on one of the US sites that was MIA for 8 days and then just reappeared one day at the nestsite with all her/his siblings. And Hurricane, she fledged and I saw her for the next two/three days and not a feather until this spring. Same with Radisson, saw her the day after fledging and then "poof" until she turned up in Edmonton.
Something may have happened but I would expect you to find the chick close to the nestsite since the chicks have only started fledging. Just as likely the chick is just further away and hanging out - remember Vesper didn't move for two days after we re-released her.
My advice, take a breath and don't anticipate bad news, it may come, it may not come or you may not get any news at all (which we count as good news btw).