I know "naked" tanks can be boring to look at, but while your little axy is sick, it's actually better for him/her. It means you can ensure the tank remains extremely clean for him/her
When s/he heals you could invest in some cheap decorations such as a hollow log and some fake (or real) plants. Trademe does have some good deals on that if you look hard enough both my flatmate and I got all our ornaments super cheap for 2nd hand but in great condition off there
(Be sure to steralise if you buy second hand and rinse well if new)
Axolotl are VERY hardy little pets... My flatmate and I have (unintentionally of course!) put our poor guys through some testing situations and they are still alive and well and thriving
It's a huge learning curve with axy even when you do a lot of research there is always still so much to learn. Just recently my flatmates golden axy got bullied very bad when we were both away (both back legs were mashed up and super gross his front leg was grazed and the tip of his tail was nipped off) and then he got fugus and lost all his gill filaments (The feather part of his gills) and he's still alive and slowly recovering
Make sure you don't do salt baths for any longer than 15 minutes. You can expect some skin flaking with salt baths because the salt is irritating to an axolotls soft skin (Flaking doesn't always occur it hasn't in our sick fella). You can also expect some stress signs during and for a short time after the salt bath. But if you do it to the recipe and no longer than 15 min then you should be fine with salt baths
Also, for dead axy, I've heard they don't float and they just sorta look like they are just still on the bottom and the only real way to tell is by trying to move them... But I've never had or seen a dead one so don't know for sure