I'm so very sorry to hear of the shock passing of Jacob and understand it must be an incredibly difficult time for you. It is only natural to want answers and I think it is important for us all (you and the vets) to understand what exactly happened.
As Jacob was an adult cat, going without food and water for that amount of time would not be considered an issue and should not have affected his prognosis in any way. We ask all patients undergoing anaesthesia to starve from the night before and, on a busy day, this will naturally mean that those patients seen later on will have gone longer without eating or drinking. I do not think this played a part in his passing.
You mention lack of lubrication, but it would have been the airways the spasmed (constricted) and these would not 'dry out' in the sense you mean, even if dehydrated (which he would not have been in that short space of time).
Before anaesthetic, it can be useful to perform a blood test to check e.g. liver and kidney function, and this would usually be offered when you fill in the consent form. However, given his cause of death, it is unlikely this would have made a difference if done.
A post mortem could help if not carried out, though it may be too late for this. This would provide a definite cause of death and shed more light on what happened.
I would advise you to write down all of your questions and concerned and to organise a face to face meeting with the vet(s) in charge of his care so that they can hopefully provide you with some more specific information.
I would also like to mention that the Blue Cross offer a very good bereavement support service for all owners. It is confidential and free of charge and can be reached here:https://www.bluecross.org.uk/pet-bereavement-and-pet-loss
I do hope this helps and please let me know if there is anything else,
Take care of yourself,