Wether or not 'mind power', whatever that may refer to can prolong life, the state of the mind does affect the length of life.
Happiness helps people stay healthy - health - 18 April 2005 - New Scientist
The link above gives an indication that the state of mind does alter the factors that usually put the 'upper limits' of human life.
Usually, what people refer to as mind power is will power, or just will. I seriously doubt that a very strong will to live could actually prolong life any further than a milder will, but I'd guess, even hypothesise that a will
not to live (in the form of depression, etc) could shorten lifespan.