If you’ve become a fan of the Google Hangouts widget and still have it, make sure to disable Hangouts from automatically updating from Google Play.
If you’ve lost it and you can grab an older APK from here, uninstall Hangouts (or hangouts updates,) and reinstall the APK you just downloaded.
The most recent update to Hangouts includes several enhancements to SMS and seems smoother, but the loss of the widget is questionable to me. Hopefully it’s an oversight, but it seems rather large to have escaped their testing.
Hangout will still function, but it just won’t be as cool in my opinion. Then again, I’m old and fear change. Boo change.