Even then, the people working on this other planet/moon will probably want to come back home to Earth at some point. Maybe a leak that way is much less likely than a leak from an Earth-based lab next to a population center, but I would bet on humans still failing at perfect safety protocols, and bringing something nasty back to Earth regardless.
As the article states, we should be clearly weighing the benefits of gain-of-function research against its risks. It seems like that was the intent of the 2014 funding ban in the US, but we never actually did that work, and that's horrifying. And if the some/many/all of the benefits of GoF research can be realized through other means, even if those means are more difficult or costly, we should probably just do that anyway.
But something tells me that "oops we created a dangerous virus now we need to seize more control" offsets that risk to the governments of the world.