Hmm, I don't know about diseases. Is it rotted? How do you water them? The one that collapsed doesn't look rotten, at least from that angle. Mine sometimes goes limp and collaps when it gets too little water, but will perk right up after watering.

I thought the same but watering did nothing. The bed stays moist I water once a day or as needed

Perhaps the rootball couldn't take up water?

Any chance of pics showing dug up dead plant? To show the roots?

I have had them in a bucket for days now to throw out so not a good indicator. I have had no loses in 2 days. Another piece to the puzzle, when I pulled them the stems literally feel off. So that made me believe some kind of rot? One other piece of information I forgot is I did feed them with miracle grow (diluted in a watering can) a few days prior. I am now afraid to feed ever again, since the remaining plants have showed no signs of dying in a few days

Well, I'm stumped.. Did the entire stem rot/mushy or just at the base? Does the top part salvageable? I'm not familiar with this species and I'm really curious whether you will be able to root the remaining stem.

Whatever it is that you do, keep doing it, sounds good for your remaining plants.. ;)

Came across this site earlier and I thought about your plants. Helpful info on what might have happened.

"Plants Wilting Suddenly, Stems Rotting at the Soil Line Signals Bacterial WiltA disease caused by a bacteria causes sudden wilting and collapse of impatiens plants. Yellowish masses of bacteria ooze out when the stems are cut. Stems are often rotted at ground level. Remove and discard in the trash severely infected plants and garden debris. Disinfect any tools by dipping them in a solution of hot water and household bleach or spritz them with household disinfectant spray. Avoid planting potatoes, tomatoes or eggplants nearby which are vulnerable to this same disease."

http://gardening.yardener.com/Solving-Impatiens

Well fingers crossed I only lost three I considered that I fed them. Maybe it was too much for them? So far so good. Scared to feed them now

Mine is in a hanging pot, 6" and it wilts right away if it dries out. I water it fully and almost immediately perks up, flowers and all. It seems that they need to be moist daily. They are more fragile than the typical impatients. Sounds like you overkilled with the fertilizer. They should be done so every 3 weeks or so and definitely not at all if recently planted. I feel if i should go away a few days and no one to water it, i will come back to a dead pot.