It's very hard to find any numbers, but it seems that most lost cats lose their lives to dogs and cars rather than to predators.
Toronto’s Animal Services report about 1,300 cats killed annually and The Pet's Tech estimate annual casualties in the USA at an approximation of 5.4 million. (The Pet's Tech seems not very reliable since it promotes glowing LED products for pets and hast the casualty numbers for cats marked with a * without actually giving a reference)
In Great Britain the reported number of cats killed by cars in 2016 and 2017 combined was 340.
Thousands of animals fall victim to Britain’s roads each year, with almost 4,000 found by local authorities in 2016 and 2017 alone, according to new research. [...] Sadly, common domestic animals such as cats and dogs also ranked highly, with 340 (9%) and 286 (7%) deaths, respectively.
But this official statistic states the number of cats found as roadkill between April and December 2017 as 143 (which extrapolates to 215 killed cats annually).
The only numbers of cats killed by dogs I could find is from Animals 24-7, seems highly exaggerated and is an "approximate, projected from media reports". They claim that pit bulls alone are accountable for killing 13,000 cats in the USA in 2015.
The approximately 3.5 million pit bulls in the U.S. appear to have killed more than 24,000 other dogs in 2015, [...] nearly 13,000 cats; perhaps 9,000 hooved animals; and between 30,000 and 45,000 small mammals and poultry.
Unfortunately, I couldn't find any official (or even non-official) numbers of cats killed by undomesticated animals.
And during all this research there were more sites reporting animals killed by shelters and their organisations than by cars or other animals... Numbers differ greatly between countries and states but it's a sad fact that your runaway cat might have a better chance surviving if s/he is not found and brought to a shelter.