Like the airline pilots, they wouldn't let that happen if they had a choice, maybe even if they didn't have a choice. Also remember, a hot air balloon burner could be an excellent weapon against any would be highjacker. If you were going to die anyway, there would be nothing left of the highjacker if the pilot had his/her head about them. Balloon burners run in the millions of BTU's.
Also, with the fire, any biologicals or chemicals would be obliterated.