Bonobo apes are some of the most impressive creatures I've ever seen. They can fully understand human speech to the point of completing complex instructions. Researchers have taught them a symbol based language that includes abstract concepts, and have quite literally asked the Bonobos what they think of death. One of the males replied that he was happy with his life, looked forward to tomorrow, and did not want to die. Even more impressive, is the Bonobos in the study pretty much taught themselves to write. When the touch screen that contained the symbols wasn't around, they took chalk and drew the symbols to let the researchers know what they wanted.
Here is one of a few videos. I don't think this one includes the part about death.
http://www.ted.com/talks/susan_savage_rumbaugh_on_apes_that_write.html
