I'm now stuck with Voice Input as the only typing mode because I accidentally chose it.
How can I re-enable keyboard typing?
You should be able to choose a default keyboard (i.e. Google Keyboard instead of Google voice typing) through your settings. Navigate to
Settings -> Language and Input (titled similarly on most devices), then select an option other than voice input. If necessary, you can deselect the voice typing option to disable it entirely. The screen should look something like this: