over time radiation would slowly go away, however if dose is high enough it wont be visible, maybe it would take 1 minecraft day for nausa and vomiting, then a total of 14 to 30 minecraft days to result in death

This might not be proper; as a reminder, minecrafts time runs faster than normal; one Minecraft day is 20 minutes

The radiation system is as realistic as feasibly possible. To make it realistic like that would be pointless considering you can die from anything else to get rid of it; immortality. This is feasible in something where immortality is not an issue; hardcore.

Your body can slowly heal from radiation but wont fully recover. its not hard to make a decontaminator