Crassula and most other succulents suffering from chronic under-watering die primarily from the top down, secondarily from the root tips back to the basal portion (base) of the stem, and the last part of the plant to forfeit its viability would be the root-to-shoot transition zone. Chronically over-watered plants generally shed the finest roots first, and continuing intervals of complete or partial soil saturation cause larger and larger roots to succumb to cultural conditions the plant is not (genetically) programmed to deal with. It's very common that the first symptom presented by over-watered succulents and noticed by the grower is a plant that simply toppled from the pot when it was bumped during watering or otherwise jostled - reason being dieback of roots to the degree that insufficient anchorage destroyed the plants anchorage to the pot and grow medium.

A tip: If you want a plant with 3 trunks, it's better to to start with a cutting that has rooted, then cut it back late spring/ early summer (in the US, think summer solstice or Father's Day to Independence day) so only 2 nodes are above the soil. This should produce 4 new branches/trunks, one of which can be rubbed off, leaving 3. OR, you can lay a branch on its side as seen in the next 3 images of a cutting started this past summer with the intent of becoming a raft-style planting:

I made the pruning cut (closest part of the cutting above) at an angle so the scar would be less noticeable. The cutting is about as thick as a fifty cent piece.

This raft cutting, a pruning resultant of removing the top of another larger specimen, can be developed so it has any number of trunks. It will now be left to grow unencumbered by pruning for a couple of years before I decide what to keep/build on and what needs to go, in terms of potential trunks. The plant is Portulacaria afra (commonly mini-jade, elephant bush, spekboom), but because it has the same growth habit and cultural wants as your jade, it might as well be one. If you're after a planting meant to evoke a sense of it being a miniature tree, one of the upright forms of Portulacaria might be the better direction, as its leaves would be much more in scale to the size of the plant. The leaves of jades don't reduce well (in size), so except for very large specimens (30"+) with trunks as thick as a Mason Jar there's always going to be the issue of the leaf size appearing disproportionately large for all but very large plants.

When pots are deeper than 4-5", we can get an accurate read on whether or not the plant needs water by using digital testers (our fingers). The top 2" of a pot 10" deep can feel dry even while the bottom 6" are completely saturated with water. What's most important is what moisture levels are deep in the pot. "Water meters/gauges" don't work because they measure electrical conductivity, not moisture. A wooden tell that can be made by cutting a 1/4 or 5/16 wooden dowel rod in half and sharpening the ends in a pencil sharpener provides an accurate sense of when it's time to water. more on that below.

Also, note the grow medium I use. Growing things immediately becomes less trying and more rewarding once we get to the point where we are no longer forced to battle our grow medium for control over our plants' vitality (health).

Al