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This sounds like it may be a fungus, though could also be thrips (a small insect).

I would recommend treating the plant with neem oil. It will address both fungus and insect issues.

These articles may be helpful:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm

https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm

It may be dead. You will first need to determine that and this article will help: https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm If it is still alive, it can regrow. Keep the soil moist (but not soaked) and try to keep its environment as steady as possible.

I would check eBay. They, surprisingly, have a huge selection of hard to find plants that you can have shipped to your home.

Wilting or dropping of leaves and softening of branches can also be a result of too much water. The soil should get pretty dry between waterings (but not bone dry) so the plant isn't sitting in moisture all the time. If the problem doesn't get better soon, it could be root rot:

https://www.gardeningknowhow.com/plant-problems/disease/treating-root-rot-gardening-tips-for-housplants.htm

This article shows some other possibilities:

https://www.gardeningknowhow.com/houseplants/hpgen/botany-911-first-aid-for-ailing-houseplants.htm

Repotting is not required for a healthy plant, but moving to a larger pot will help the plant grow larger and may help it grow to fill in any bare spots. If you want to keep the plant the same size, keep it in its old pot.

https://www.gardeningknowhow.com/houseplants/hpgen/learn-more-about-repotting-houseplants.htm

You can prune back the bare stalks, as described in this article:

https://www.gardeningknowhow.com/houseplants/aralia-plants/polyscias-fruticosa-ming-aralia.htm

As for the watering issue, simply resume your usual watering schedule. The leaves should recover; if they don't, you can prune off the dead portions.