Race Start Procedure when everyone pits on Formation Lap

Question

During the 2021 Hungarian Grand Prix, after the initial start was red-flagged due to a turn one incident, the field started their second formation lap, with all cars on intermediate-wet tyres.

It became apparent that the circuit was drying rapidly, which prompted all of the drivers, except Lewis Hamilton, to enter into the pits to change their tyres for slicks.

In the situation when cars start from the pitlane, as is the case for all-but-one of the drivers in this case, the rules state that they must wait at the pit exit line until the on-track "field" have passed before they join the track and start racing, as stated in Rule 36.2 in the Sporting Regulations:

[...]

However, any car reaching the end of the pit lane after the five (5) minute signal must start behind any car already at the pit exit.

All such cars may then join the race once the whole field has passed the end of the pit lane for the first time after the start.

But what is the procedure if, in this case, Lewis Hamilton had pitted too, as there is no "field" to pass the pit exit? Do they perform another formation lap, and regain their qualifying position, or do they all start the race from the pit exit as they line up?

Answer 1

Literally answered here: https://the-race.com/formula-1/how-hungarian-gp-would-have-restarted-if-everyone-had-pitted/

From the article:

The final car into the pitlane would have been the equivalent of the final car taking its position on the starting grid.

When that car entered the pitlane the start signal would have been initiated, with five red lights turning on and being extinguished.

Once that happened, the green light at the pit exit would have shown and the field would have returned to the track in the order they lined up at the exit.