Angels

I just had my pet angel kill enner for me THANKS MORTIFER FOR SENDING ME A FRIEND!

Question: This particular angel has been following me the whole game. Do all angels dissapear eventually or do some of them have some kind of permanent maker that makes them stay forever?

My understanding is that angels who appear when you make a sacrifice are permanent, whereas angels that appear when you pray are not.
Don't make them carry your stuff across the world map . >_<