This was an interesting study and I am not sure what to make of it: “What’s perhaps most interesting is that changes in gas prices, “had little impact on hybrid segment loyalty,” according to Polk. In the company’s quarterly hybrid analysis from 2008 through 2011, loyalty rates ranged from 26.4 to 41.8 percent, but spent most of the time in the 30s.”

Maybe it is the cost of the battery that contributes to the loyalty:
A: It should be noted that the Prius traction batteries are under warranty for 8-10 years or 100,000 miles, and so will be replaced for free before then in the case of failure. However, should the battery fail outside this timeline, the estimated cost of traction battery replacement is $3,000.
http://www.toyotapriusbattery.com/faq.html