You can try to save it if you wish. First unpot it and look for mushy rot. If you see it, toss the plant. If all looks firm, including the stem, get a clay pot with hole-- smaller pot than the one it's in. Purchase commercial cactus/potting mix and a bag of perlite. Rinse the perlite through a strainer to get the tiny particles out. Combine the mix and perlite 50/50. Repot, a little higher than it is now. Don't water for 4-5 days. No direct sun, bright light. When you do water, let it run out the bottom, then don't water again until it's dry.

The stem and the root system of this plant is dead. You can try re-rooting the rest of the plant by cutting off the stem above the dead tissue. You need to cut to healthy tissue. Then let the cut dry out for several days in cool, bright shade. Then empty out that little pot and fill it with fresh new cactus/succulent soil, preferably with added pumice or perlite. Do not water it. Put the cutting into the soil and the little pot into bright shade. Mist the foliage with water lightly and frequently and wait. The plant can grow new roots. When it has some roots you can start watering the soil. Let the soil just dry out before watering again.

I don't know if this helps you or not...but, one thing i've come to learn from living all over California and having grown may succulents of all types for many years is that you must learn which micro-climate you're growing in. California is huge so knowing this is key to success in my observation. In the La Jolla area we get a maritime layer which some of my plants thrive in while others do not. We are at the mercy of what they call "May Gray," and "June Gloom." Find ways to anticipate this and protect your plants as best as you can. Now that we are over "the drought" i have to safe-guard my plants from the deluge of rain we now get in our winter-time. Knowing this now i make sure my soil is quick-draining and in a grittier mix. If your plants appear the same day after day, week after week etc., make sure they're not in a state of dormancy. Aeoniums for example are summer-dormant so i do not water them. They flourish again in cooler temperatures. If you're really having an issue choose a plant and remove it from its pot and thoroughly inspect the roots. Make sure the root system is healthy and insect-free. Many plants stop growing when attacked by insects. Many plants also seem to enter a sort of "stasis" when too hot or too cold. My echeverias for example have curled into a ball due to the excessive heat. This is the way the plant protects itself. They will "bounce" back when the temps cool off a bit. Compare the growing conditions you currently have your plants in to the native environments they come from and adjust as best you can. Absorbing all this will find you one day with all the skill you need to grow your plants successfully. You will know exactly what to do and when to do it. Time and patience will soon pay off. There are many forum members here so full of knowledge and a wealth of experience i am still amazed by it. I still also show up here to learn more from them. --All the best : )

I also questioned size of pot in my original post, but didn't say that you should use smaller one. Karen is right. If you find that plan is tipping pt over, you can place a larger rock or 2 on top of the mix. I use large rocks to support newly repotted plants, but they can be good counterweights too. Or use pot that is not so deep but wider at the base, so it is more stable. Terracotta/clay pots are also more stable, because they are heavy. I use mostly plastic for that reason. I also mentioned that I would cut of leaves that are mushy - didn't say that you should since I really can't see the mushines in your photo. I keep succulents in smaller pots. Not because "they like it" as some ppl suggest, but for lack of space. If plant gets too big, I rather divide it and give away some. The reason I do not grow Aloe vera - it's leaves grow quite long... I know that pp used put some rocks or pieces of broken terracotta pots over drainage hole to prevent mix from falling out. Use piece of window screen or any other mesh with small openings. Or even piece of landscape fabric (it lets water thru), or coffee filter. Even piece of newspaper will work, but it will decompose.