The three days the Sun is dead during the winter solstice is very plausible and thanks for all your other ideas. Also like I mentioned the moon is out of sight three days per month too. What’s interesting is that in early religions ideas neither the son god or moon god is the one that dies. The only exception is Osiris in his later mythology and possibly Mithras but there not much in any writings about him going back to Persia where he was originally invented and worshiped.
Some say Horus also a sun god was dead three days after being killed by Set but again no verifiable sources.