they channelled the Dark Side of the Force into the blade of plasma crystals)
That's debatable, because the side of the Force is with the case of the user. There is no chaotic corruption if you pick up some other blade, as you would get tainted for example in WH40k universe. So it's wrong to claim that and another point comes with the plasma. Sure you can store inside a magnetic bottle, but the sabre's that we've seen doesn't work that way. They might have at the beginning, when they were complicated pieces. The modern and standard models flow the force through the kybercrystals and ignite the blade in that way. Force then keeps the blade steady and gives it certain characteristics, like for example Ren's chaotic spits in his crusader blade.
The thing here is that SW is fantasy, even though we have replicated those crude forms and made them reality. Like in this hacksmith example,
Essentially, lightsabres are equivalent to the classical fantasy magical weapons, including blades. In their own way, they are taken to extremely close to their scientific counterparts and that is through the artistic interpretation, instead of basing it on the science. And like I said previously Sabine's checked through the critical eye, the fatality would have removed the MC and therefore Sabine needed story shield. However she's not the only one who have survived hits or even dismemberments. Vader is the best example of extreme survival. Not only he was dismembered and Kenobi refused to deliver a killing blow. Instead, he left Anakin/Vader to suffer extreme burns at the bank of a lava river.
The Emperor came to rescue him later on after Kenobi had left and even in his case, it took a while before he was on the surgeon's table. Sabine was found by Ashoka pretty soon after the hit and Lothal Capital isn't really that far away from the comtower. You have to watch Rebels to realise the distance, but let's just agree that the tower is within the greater capital area. Ashoka was also trained back in the Old Republic days and I'm pretty certain that her training included medical procedures for the sabre victims, because during the Clone Wars there were so many of them.
That knowledge is not forgotten, and certainly not in Lothal, where they had the main rebel camp for a long time before they moved the base to the mushroom planet. They also had the famous Jedi Temple, including the mysterious Temple Guardians. So the knowledge to treat the injuries is definitely there.
Only thing that I agree is the wound and miraculous healing from it. Sabine should be suffering more, but then again, we don't really know what medical procedures they did to her to get back on her feet. We also don't know really for how long it was between the hit, going to the hospital, and feeling good enough to get back on the feet. Who knows she might be on the good stuff, but House of Mickey is not going to included drugged-to-the-eyeballs in the fantasy series, because there are no addicts in the SW. It's a dark fantasy that ignores some hard realities.