A Disneyland spokesperson has confirmed to local media that RunDisney Events in 2018 and beyond have been canceled at the Disneyland Resort:

Quote Originally Posted by The Orange County Register
RunDisney, the Walt Disney Co.’s race organization, announced Wednesday, Oct. 18, that it is canceling its half marathon and other races at Disneyland Resort beginning in 2018.

Races at Walt Disney World and Disneyland Paris will remain.

... runners who per-registered for [Disneyland] race events in 2018 will receive a refund.

... Disneyland will host its last runDisney event for the year on Nov. 9 -12, the Super Heroes Half Marathon weekend.
The Disneyland spokesperson cited the on-going multi-year construction period around the whole resort as the reason for the cancellation; however, it is rumoured that the Disneyland Resort and Orange County could not come to terms on the conditions of new permits required to hold the event on county roads.