Any fire is "Land as soon as possible", whether extinguished or not.
Any fire you can't extinguish, or can't be sure you can/have extinguished (as would be the case with Li fires) is "Land IMMEDIATELY"
Pretty straightforward diagnosis in my book, at least.
However, is the "ditching" going to be survivable? Landing a heavy in forest or mountains is certain suicide so better take your chances. Ditching in water? Your call, you've got a life and death judgement to make based on poor data.
Me. I'd tend believe a modern fire warning system.
But you decide...You're the Captain.