Wait.... If I'm reading this correctly...
Is there an ending where everyone keeps their lives? And if so how do I get it?
There is such an ending!
Multiple such endings actually!
For an incredibly simple such ending just like... leave the school and don't prefer the evil spooky ritual.
For the BEST ending... you'll need to befriend the girls and get them to join you for shenanigans... then explore a bunch, and open certain doors and certain times.