Salvageable! Check the soil, it might need to be repotted, especially if the soil is dry and/or compacted. Other than that, water roughly once a week and keep it in a sunny window.

You can also take a cutting and put it in a glass of water as backup. Make sure to get at least one node (the wider area in the stem, usually with a little nub of aerial root starting). Cuttings with leaves attached will have an easier time.

Absolutely not, it’s just a bit leggy. You can either cut the individual pieces and replant them in dirt and they should sprout roots after a while, or you may be able to put them in water for a while (this method takes longer). As long as there isn’t any rot anywhere

He'll be fine. Mine had one sad, dry branch and now he's a jungle princess. These things are very robust and can regenerate from big neglect.

Not too late. Clip off the spindly bits. Two options: cut into a few sections, it turn in water until they root then replant. Or, cut it into sections where there is a node in each section. Lay the sections flat across the Silk with the node facing down. Water lightly - like with a spray bottle every day until the nodes root and leaf. You can put cinnamon on the cut ends which acts like a fungicide. It you can find root growth hormone I find it helps jumpstart the rooting.
Good luck!

This appears to be a pothos but I could be wrong. Either way, the below suggestion should work.

If I were getting this plant from someone else and knew nothing about it, I'd cut all the stems leaving 1-3 nodes on them stem and at least one leaf (if you can) and I'd put them all in water. Wait a few weeks and when you have 2" or longer roots, get a pot that has drainage holes, get new indoor potting soil, plant your plant in said soil, and place it in bright indirect light.

As far as care, I stick my finger in the soil every few days and when it's dry 1-2" down (for an average pot size nothing super tiny or huge) I'll water the plant over my sink making sure to water it very deeply.

I'm no expert by any means, but I've seen plants come back from much worse. It's worth a try.

I would check the roots. Something is certainly wrong, but I think it has a chance. If the roots seem to have rotted away, I would take a cutting like suggested by @Thebazilly@pathfinder.social and start fresh.