You can't get away from santa or at least it's not very clear how. He also seems to always notice me instantly in the first sighting which makes it impossible
You can get away from him, you just need to stay out of his line of sight long enough for him to lose you. Santa instantly chasing you at the beginning of the second map is a bug that a few people have run into, I think it is caused by being killed in that map and then respawning. If it keeps happening, crouching down and hugging the wall seems to stop him from seeing you. It only ever happened to me once during development and I've tried to fix it but it is very hard to reproduce. Download the updated version and see if it happens again, I changed around some of the code in hopes of fixing it but as I find it so hard to reproduce the issue I'm not sure if it has been fixed or not. Sorry about the inconvenience.