even if someone hits a deer (or a squirrel, or anything), isn't there still a legal requirement to stop?
if someone claims that they thought a cyclist was a deer... that sounds like an automatic inattentive/careless driving charge... which should help firmly establish fault so the cyclist's family can use the civil courts to relieve the driver of all worldly possessions.
this is where i'm ideologically torn when it comes to harsh criminal charges... on one hand the driver could face prison, huge fines and huge legal bills... on the other hand, they could just be given a traffic ticket and then cleaned out in civil court. not that the two are necessarily exclusive of each other, but there may not be much left to take after a big criminal defense. my guess is that the prosecutor(s) is discussing the options with family before making any decisions.