How much does it cost if someone falls ill before take-off? A month or so ago, I flew from LHR to Australia, via Doha, on a Qatar Airways A380. Just as we were about to enter the runway at LHR, the captain announced that someone had been taken ill on the plane, and we'd be going back to the gate. That delayed take-off by (I think) about an hour, and required topping up the fuel tanks.

How much would this have cost the airline? Are there any circumstances where they would pass the cost onto the passenger who fell ill?
It's hard to get an exact figure, there are fuel prices, the time to taxi, gate charges, medical charges for the removal of the person on the plane, staff costs, and more. I can't guess at most, however from a fuel cost perspective I know for the 747-400 at LHR many airlines use a figure of 1000kg in planning for APU and taxi to takeoff. An A380 would be more, I'd ball park a figure of 1380kg for the airbus based on the MTOW difference (a rough approximation). 1380kg is about 1750 liters, at about .50 GBP per liter that's about 875GBP, or about 1150USD at today's conversions. So the fuel alone would cost somewhere around a grand, I'd imagine you could comfortably double that by the time all is said and done. 

As for passing the cost on to the customer I've never heard of that being done for a genuine illness, or even a suspected illness. I don't know if they could if they wanted to, however I cannot imagine them trying it, the reputational fallout would be enormous.