The longer you wait the more harm done by the fertilizer sometimes it doesnt just happen over night but prolonged exposure will burn the roots. Flushing would take forever!
Dont do leaf cuttings unless you think the plant is on its way out it isnt the easiest thing in the world to get them to take root either.
Just keep it simple take the plants out when you do pour some water in a bowl take the plants and swish them around to get the soil off of the roots its a good way also to make sure you dont damage the roots
They will be fine just dont wait too long like I said, the longer they are exposed to the fertilized soil the more they are at risk of kicking the proverbial bucket.