Google also could cut off Mozilla's funding in a heartbeat. Since their management is incompetent (but their engineers are awesome and I love them), they haven't done any serious attempts to diversify their sources of income, or at least to put some of that cash away for a rainy day. Firefox is just as dependent on Google as are any of the Chromium rebuilds. (I am writing this as someone who has been using Firefox since about 2006 non-stop, seeing its market share drop by a factor of ten in that time).

Google does some stupid things, but Chromium is "too big to fail" at this point and it's too essential to products like Android which are also at that same point.

But hypothetically if Google stopped contributing to Chromium the project would be forked and it would live on. Frankly, Google removing themselves from Chromium would fix the one major complaint a lot of people have with it.