From AV Herald
The aircraft fire is unrelated to the batteries. This will be confirmed tomorrow in a boeing press conference. Fire is strongly believed to be as a result of galley overheat - failure of coffee heater trip switch which was left on.Burnt out much of the galley and area above causing deep damage to aft bh and rudder/elevator system.

Ah, Very convenient. I find it strange that you don't really know what plane type you will be flying on when you book. If the fleet isn't grounded, I for one would be circumspect at flying on one of these.
I would imagine an in-flight fire is a terrifying experience, even worst than a ships fire. I don't think I would be happy flying in one of these at the moment. Lithium-ion batteries are meant to really burn when they do catch fire, a Kers fire burnt out the Williams pit garage.
I see Boeing shares have taken a hammering. The fire was apparently caused by a left on empty coffee percolator where the safety trip didn't. It has apparently caused extensive damage to the rear of the aircraft including the tail area and their control systems.
I would imagine if they are grounded again the airlines would temporally keep in service aircraft they were retiring or they would replace them with short term leased planes.