sudo killall coreaudiod made it so I don't have any sound at all

sudo killall coreaudiod should work to kill your audio drivers. It should reload itself within a fraction of a second. (verified on my mbp running 10.14 but used this on a couple of previous versions)

You can also use the command:

sudo launchctl kill SIGTERM system/com.apple.audio.coreaudiod

This command will do it:

sudo launchctl stop com.apple.audio.coreaudiod && sudo launchctl start com.apple.audio.coreaudiod

Details

Martin Strouhal's answer doesn't work for OS X/macOS ≥ 10.12.4 due to removal of com.apple.audio.coreaudiod from system integrity protection's RemovableServices whitelist in /System/Library/Sandbox/com.apple.xpc.launchd.rootless.plist [1].

sudo launchctl unload /System/Library/LaunchDaemons/com.apple.audio.coreaudiod.plist
/System/Library/LaunchDaemons/com.apple.audio.coreaudiod.plist: _
   Operation not permitted while System Integrity Protection is engaged

So instead of removing (unloading) the service, we instead just restart it.

Also, the latter command (sudo launchctl start com.apple.audio.coreaudiod) worked to restart the service after I had killed coreaudiod using killall coreaudiod.

You need to reload coreaudiod instead of killing it. This one-liner will fix broken sound without restarting your mac

sudo launchctl unload /System/Library/LaunchDaemons/com.apple.audio.coreaudiod.plist && sudo launchctl load /System/Library/LaunchDaemons/com.apple.audio.coreaudiod.plist

You've simply killed Core Audio, which will restart itself if you restart your computer. Try logging out/in, and if that doesn't work restart your computer.