CarbonSeed: Yes, like Marakinta says, the game has permadeath and it isn't optional.

The indicator of how many times you need to die before to get the permadeath, and be definitely dead is a mark, like a necrosis or something like that in the body of Senua, that mark grow everytime her get killed and if the mark reach her head, everything will be over. So that way you can, barely, know how many "lifes" remain to you, but there is not a more clear indicator of that.

Quawerty: Finished the game, combat difficulty on Auto.

I got the warning about permadeath and I sincerely feared it. Most of my deaths occurred during fights, although few occurred in a different way.

The necrosis on her right hand should tell you how bad it is. It grows most of the times you die. But sometimes, it fades back.

I don't know if it really is there, but believing in it made my struggle on her journey much more intense.

It is the matter of trust. I trusted the devs it is balanced and let me finish, if I try hard enough. So I tried.

MrFuzzles: Without spoiling too much - and I'm assuming that people clicking this thread title are already looking to spoil this particular aspect - I can point out that what the game tells you is not a lie but you will not find anyone who has had their experience ruined by it. You can google it if you want I guess, but it's intended to give you a bit of anxiety and you will ruin a late game reveal by looking it up.