Senua is in fact a minor goddess.
Acting on the assumption that all or most of what we see really happened, then Senua faces down several gods or god-level monsters, including Surtr. Surtr is a fire giant who is a key figure in bringing about Ragnarok and dooming all of creation, and that event is supposed to be inevitable, according to Norse myth. Two explanations fit how this was done. First, Senua did some insanely high-level Cthulhu Punching. The second is that Senua is a nascent goddess coming into power she doesn't even realize she has, since the scale of what she's facing is so great, and her own fear and doubt is so strong, she can't even recognize how impressive what she's doing really is.- Remember the origin of Senua's name. It's actually the name of a little known Celtic goddess, discovered in 2011.
Regarding permadeath
The permadeath warning is meant to scare the player, and preliminary testing indicates it either doesn't exist or is extremely lenient. But, right before the final battle, the voices wonder what happens to them if Senua dies. At the end, the voices get quiet, the narrator states they can't go on anymore, and urges the player to follow Senua. Permadeath isn't about the player, it is about Senua's psychosis/the voices. By the end of the game, they are "dead" and Senua is left to go her own way.- The story about permadeath was created by the developers as yet another Mind Screw for the player: permadeath and the wiping of the save files if the rot present on Senua gets to her head wasn't a real threat, but making the players think it was would cause a genuine sense of fear and paranoia in the player, having them experience a bit of what Senua would be experiencing.
Also assuming that everything really happened, Seuna did save Dillan, in a way
. She may not have brought him back to life, but she freed his soul from Hela's grasp and enabled him to move on. The mythological aspects of Senua's journey were fabrications of her mind
Senua did travel to a Norse settlement, but it was abandoned and/or destroyed by one way or another; it wasn't actually Helheim. Additionally, the warriors she fought were the vikings that razed her village. She unknowingly tracked them down and killed all of them.