How can I save this Shifalea plant?

Did you drown it? Remove remaining plant, place in a glass of water. Throw out the soil in the pot. Soak the pot in vinegar overnight or at least 6 hours. Rinse the pot and let dry. Place new potting soil in the pot with drainage rocks underneath. Replant the plant.

Appears not to have any soil in the pot for the poor plant! Try to separate healthy, green piece(s) from the rest of the plant, roots and all. Throw away old pot, dirt and rest of plant pieces. Replant in a new pot with new soil. (I put a handful of brown, dead tree leaves in bottom of my pots, when re-potting, to keep soil from falling through drain holes & also helps fertilize plant as leaves decompose.) Plant as deep as you can in pot covering most of stem(s). Fill pot with soil leaving about 1" of the pot at the top. Water and set in a bright window, it does not require a lot of sun. It should grow into a beautiful plant again. Water only when dry.

The plant definitely needs repotting, I don't see hardly any soil in the pot and can see roots down there. Rinse the remaining soil off the roots before you repot it. Clean the pots and rinse with vinegar and let it sit for a few minutes to get rid of any remaining bacteria, mold/mildew and other bad things. Rinse the vinegar off well so it doesn't get into the soil and kill the roots. As Mona said, put down a good layer of rocks for drainage, then new potting soil and replant the plant. Care for it, but watch that you don't overwater. Wait until the plant starts growing new leaves or shows signs of being out of repotting dormancy before you fertilize. Hopefully that will help the plant to grow again.

I will try that

Really doesn't look too bad. This is called Schefflera/Hawaiian Schefflera. Common Names: Umbrella Tree, Australian Ivy Palm, Octopus Tree, Starleaf. Put plant in new pot only 2-3"s larger(wide & deep) add fresh good potting soil to bottom & sides not much on top & not up against plant base,using sharp pruning shears or knife or shears trim off all dead stems down to crown(base of plant)place in really bright light no direct sun water thoroughly only when completely dry, make sure new pot has good drainage or use clay/terra cotta(soak terra cotta in water before putting plant in it) make sure you have good water proof saucer to protect floor;give plant some water soluble miracle grow fertilizer(green granules) 2x year during regular watering schedule. It just needs some attention but don't over do it most houseplants die from overwatering & too much crap done to them. Do not remove disturb roots, do not remove old soil and definitely do not rinse the soil off with any vinegar or put roots in vinegar(vinegar is used as weed killer) it will burn it go into shock and die.It's all ready going thu some changes by trimming and transplanting. if you cannot get nursery black pot off easily cut it off with sharp knife or scissors trying not to mess up disturb roots too much. It will be fine actually looks healthy just needs soil and a trim. you could use same pot if you do not have another just tap sides to loosen plant pull out plant fill bottom with fresh potting soil then put it back in pot and cover top some to fill it in not too much do not cover where it meets soil/base of plant.if you get fungus gnats from new potting soil(many times it is full of larve) get some mosquito bits( from any store hardware or garden, online) let soil dry out then cover top of soil with mosquito bits then water well it will kill them off in just 2-3 days. may need to repeat in 7-10 days so do not water inbetween plant will be way too wet. plants/soil are much better off on drier side than overwatered. Do not change location put it right back where it has been growing. This plant is TOXIC to cats & dogs-- contains calcium oxalate crystals that can cause oral irritation, excessive drooling, vomiting, difficulty in swallowing and intense burning and irritation of the mouth, lips and tongue in pets who ingest.

Wow you certainly know alot about plants!.Very thorough. I'd better get to work! Thank you