Although if the issue is based off staff, I fail to see what cutting the London service would do.
Pros: You save money... that's about it. Since the morning trip is so early, you can't strategically cut down the London trip to reposition a staff member elsewhere, and as such there's no benefit to cutting the service in the midst of a staff shortage. The only thing I can think of is maybe you can use that staff member to potentially run a counterpeak service in the evening? That's about it though.
Cons: You completely kill any faith in the extension. You're basically admitting that the pilot failed, and you potentially kill any chance to bring GO to London anytime in the near future.
In other words, even if we ignore the politicking, there is quite a bit of logic to keep the London service.