In my opinion, I think it would be a pretty big blow to the timeline of the plan. It could delay launch indefinitely. Outside of this board, I have no doubt that there are many potential investors waiting for this news.
I'm remaining cautious, but I highly doubt that Verizon will explicitly say no. Instead, I think they will demand a ridiculous amount of money to provide the service. Probably much higher than the other carriers. I also think that if GoIP Global did their homework, they knew this going in. So it's probably an issue with trying to negotiate a better deal and locking in the contract long-term so Verizon can't jack up rates anytime soon.
If it did fall through, GoIP could setup a regular phone number and run the service through that. It would function exactly the same but without the convenience of texting GO800. This would provide a band aid until contract talks are resolved.