It can be both countable and uncountable.
If it's countable, it refers to a single instance of life. 'Lives' refers to multiple lives.
If it's uncountable, it refers to the concept of life in general.
The same applies to a lot of nouns.
You could say "Life without friends...". In that case, the sentence still works whether or not 'life' is countable (as long as you make 'friend' appropriately plural or singular).