Hello Amanda, it does look bad. Base rot really goes through the core, so oftentimes it is like a death sentence.
But in the interest of experimenting, don't know if it will yield any favorable result since the rotting is just so pronounced, you can try unpotting it, and remove all the leaves with rotted ends, cut off the rotting portion of the stem till you get to a good fresh part. Set it aside to dry out, apply some cinnamon on the cut end, position in part shade, and wait. Sometimes, though not always successful, the plant may still try to callus the cut area and regrow new roots and then slowly new leaves. Don't put in soil right now, just let it air dry and wait. The seasons are changing now, getting cooler. Some of my echeverias are actually happier at this time of the year than in summer when it is baking hot here.
Now if it does start making new roots, then you can put it back in soil, but make that media grittier, the roots system of this plant grows so shallow and quite thin, so it really hates staying too wet. That is why I add more pumice or perlite in the cacti soil I use and I further top dress with poultry grit (insoluble crushed granite) to protect the base of the plant from staying too moist.
Good luck on your plant! If you lose it, don't feel so bad, sometimes it is a learning curve so you can avoid the same pitfall next time.