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.

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.

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

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!

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.

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