As for whether thought exists independently from language, it depends what 'thought' is to you. I'm currently using my fingers to type - what I'm typing is governed by language, however, how I type it isn't governed by language at all. I can do many things which require no linguistic ability whatsoever, but you could say they require thought.
Even with more higher functioning thought, a distinction has to be made about what is language and what is a concept. Concepts aren't language. For example, the concept of object permanence - that an object out of sight still exists. This develops in babies before they have any linguistic abilities.