By the S3 finale, Rudyard and Antigone are beginning to tentatively discuss the possibility of going into a different line of work, and by the end of the episode Rudyard’s been offered a job working with the mayor’s archives, which he seems enthusiastic about.
Even without Chapman’s rivalry, it’s established that the Funns were already struggling financially and it’s reasonable to assume they wouldn’t necessarily have chosen the funeral business, had it not been in the family. Taking all this into account, along with the fact that the writers have said the 4th series will be the last, there’s a decent possibility that they’ll decide to pack it all in by the end of the series.
As for Eric, fans have pointed out that funerals seem an odd choice for him, given that his talents would likely be suited to planning celebrations for less sombre occasions, such as birthdays or wedding anniversaries (although we can likely assume that his choice relates to something that happened... a long time ago.)
Eric’s brand of funerals tend to have a celebratory air about them, which is fine for people who prefer to frame it as a celebration of the deceased’s life, but not so much for anyone who expects a more sombre affair. It’s also been established that Eric has a hard time understanding or dealing with others’ grief.
After the events of ‘The Sunshine Treatment’, Eric might come to the conclusion that he’s not as equipped to deal with bereavement as he’d assumed, and that his talents would be put to better use as a standard party planner (or running one of the various establishments he’s already set up in the village). This revelation would coincide with the Funns deciding to close up shop, leaving Piffling Vale with no funeral home to speak of, and rendering the Funn/Chapman rivalry ultimately All for Nothing.