Oh but there is for those who seek it!
One kind of proof is called dimethyltryptamine. It lasts for 10 minutes, but when you come back, you might have a radically different view on these matters.
Other psychedelics, like LSD, also offer a different perspective on life and death and there are also different kinds of spiritual work one can do - meditation, holotropic breathing or living life in nature. They all help you realise just how fragile and transitory life is in nature and that that is a good thing.
>Religions and mystics have been exploiting the normal human fear of death
Isn't science (or rather scientists) driven by the same fear ? Isn't the knowledge that we're going to die a factor in making us go out and do stuff to survive ?
Wouldn't immortality lead to a state where we'd have to invent a simluation of mortal life in order to actually feel alive ?
How can one tell that this life isn't such a simulation ?