It would be advisable to wash the open wound with a Savlon solution every day to keep it clean (just syringe in and let run off).There may be more maggots in him/her, I would clean clip a wide area to make sure, not just the actual spot you found them.
Then when it heals the skin will crack, I used udder cream to keep it soft last year (Had a bad case here too, but you wouldn't know now!).
Hope the little one comes right, it is surprising how often the flies attack in clean fleece and you will not see it until the lamb kind of gives in and behaves differently.... it made me feel very guilty last year.