Really unlikely anyone would die from the experimental vaccine itself (at least in terms of the disease it is based on). Vaccine would be made from inactivated and/or weakened stock.
As far as the vaccine "not working" -- that absolutely is possible. 70-80% protection (that percentage of vaccine recipients would not contract live disease) would be seen as a great success.
Especially since we are already testing Ebola vaccine on humans in the United States.