Context: after eating a death cap (Amanita phalloides), you’d notice a few of the symptoms at first, but these usually resolve after a day or two. After this, you’ll enter a latent phase where you feel fine, but your liver and kidneys slowly start to fail. By the time you notice, it’s usually already too late.
The damage is permanent on a cellular level - the affected cells will either die, or in the case of radiation exposure, can become cancerous instead. If you got a small enough exposure, and immediately sought medical attention to remove the toxin from your body in the case of amatoxin ingestion, then only some cells will be affected, and maybe your organs can continue functioning and eventually recover after the affected cells die off. If the damage is significant, you might survive if you get a liver transplant and dialysis, since the liver and kidneys are the most affected due to their role in filtering and removing toxens.