To be honest the two best phrases to use in airfrreight are....
" No responsibilty due to mortality by natural causes"
and
" Warsaw Convention, $20 per kilo.....""
Animals die onboard aircraft, and it's nothing to do with with pressurizing/heating holds. The stress on the animal sometimes does it.
More to the point look how many people die on passenger aircraft through factors other than flying, then factor it into the life expectency of a dog......
The lawyers wil get nothing....