Even without incident, many movies with heavy special effects can take up to a year to finish the final draft. I kinda suspect it's by design. Get the studio hooked and ask for more money to increase the production values to match the acting.
Paul Walker is probably the most recent one to fall into that category. I believe his character will be in the next Fast and the Furious movie, but it'll be a CGI role (with family members standing in as the body/face they CG-enhance)