Is it wise to use a cat sedative to calm your cat, and help them sleep on the long trip?
For airplane travel the answer on cat sedative is almost always no.
It prevents you from taking a step into the unknown future you are facing.
In the case of pet loss, there is an underlying denial, a refusing to accept the loss of a beloved pet, or refusing to accept the way it happened.
Then, people like Roberta, James, Sonia, Jon, and yours truly will provide guidance and suggestions.