There should never be a need to do any flushing of soil. The only time you'd flush is when you finally realize you've added to much fert. The plant that is dying received too much fert. There's no guarantee that flushing gets the ferts out of the soil. The best thing to do is to understand how to grow plants properly and not deviate from that knowledge. There a scientists that have spent their whole lives understanding plants. Those are the people to listen to, not folks in an anonymous forum. Not even me. What I've tried to bring here is what I understand of plants after reading text compiled by various people who work in the science of growing plants. That's what everyone should do. It's hard to see exactly what's going on with plants unless there are photos. This website is so bad now that people are losing interest in it.
For plants that are dying, perhaps the best thing to do is to take some cuttings that still look good and try to get them rooted but using rooting hormone like Clonex. That way you can basically save the plant but you'll have to wait for the little one to grow up.