fixed sentient diseases reinfecting when dead (#60107)

code/modules/antagonists/disease/disease_disease.dm

@@ -5,6 +5,7 @@
 	viable_mobtypes = list(/mob/living/carbon/human)
 	mutable = FALSE
 	var/mob/camera/disease/overmind
+	var/disease_id
 
 /datum/disease/advance/sentient_disease/New()
 	..()
@@ -38,6 +39,7 @@
 /datum/disease/advance/sentient_disease/Copy()
 	var/datum/disease/advance/sentient_disease/D = ..()
 	D.overmind = overmind
+	D.disease_id = disease_id
 	return D
 
 /datum/disease/advance/sentient_disease/after_add()
@@ -46,7 +48,9 @@
 
 
 /datum/disease/advance/sentient_disease/GetDiseaseID()
-	return "[type]|[overmind ? overmind.tag : null]"
+	if (!disease_id) //if we don't set this here it can reinfect people after the disease dies, since overmind.tag won't be null when the disease is alive, but will be null afterwards, thus the disease ID changes
+		disease_id = "[type]|[overmind?.tag]"
+	return disease_id
 
 /datum/disease/advance/sentient_disease/GenerateCure()
 	if(cures.len)