I've deleted the GV Mobile app. So yes, it can be done. You lose some of the features, but nothing with the texting functions.
The push notifications were very fast. I only tested by sending texts from the Google Voice web interface on my MBP, and all were received within 20-30 seconds. Just to point out, though, speed of delivery is dependent on the TextNow servers and their load....
Sending from TextNow app back to when they showed up on the GV web interface was just as fast. Didn't have a second phone to text them to.
I use iBlacklist for call blocking, etc., so the extra GV # will come in handy in the future.