I am not sure it is coming back. In fact, the website for the mortuary has been pulled from the internet also.
In doing a Google search, I did find a post on the A&E message boards that was dated June 8, 2006 and it did say that the show was not picked up for another season. It was from Viewer Relations at A&E TV. So I guess that answers that question.
In that same thread, someone posted that they were in San Diego on vacation in July, 2006 and went by the mortuary to see everyone only to find out that Shonna and Chuck are no longer there. Rick and David were off that particular day. Emily was the only one there and she did not want her picture taken.
There are a lot of posts there, but here is the link if you want to go and read them all: