This was a brilliant plan by Ferrari. They really did their homework. There is nothing in the rules preventing it aside from the unsafe release penalties that Formula One has already assessed to Haas. The Haas cars should have been stopped before they got out of the pit and onto the track. I've seen it done many times over the years but that wouldn't have provided the desired results. With the new rules, they can't claim a technical failure of a part that has a limited replacement like the ECU. Crashing costs more money and can damage a gear box which is another limited component.
From the Formula One website;
The cars are timed by loops embedded in the track. Once Vettel crossed the last loop before pit entrance, he could speed up because he wouldn't cross the next loop. I don't know how many segments there are. They provide information during practice and qualifying for 3 sectors. If they only use those 3, Vettel had a considerable distance that he could run faster than the other cars prior to leaving the track for the pit.
The track in Australia has a fairly long pit entrance where there is no speed limit and a fairly short distance where there is a speed limit. As you see on the map below, the path through the pit is shorter than the path on the track. Being able to drive at a higher speed than the cars on the track gives an advantage.
They didn't wait for the wheel to fall off. They pulled off to the side in a place where there isn't a place to park the car safely. There was no reason to stop the cars. They were still running. There have been cars that lost wheels or tires and drove back to the pit. There were a number of places they could have driven to where the car would have been out of the way but they chose to stop in a place that would require the virtual safety car so they avoided your 100 to 1 chance.
I would say that the odds of the same error happening on two successive pit stops
is astronomical.
As I said earlier, even if Hass and Ferrari were to admit they did it on purpose, there doesn't seem to be any more that F1 can do. I'm sure there will be changes in the future. The virtual safety car is a relatively new tool that doesn't seem to work well. It leaves the cars spread out around the track so it doesn't leave a long period without traffic like the normal safety car does. They need that time to get cars off the track safely.