There are still some very viable niches where film can do well, IMO.
There are a variety of very successful people who use film, here are a couple examples.
A few of the advantages of film is that it is forgiving, produces beautiful work, and getting professional backend work done is simple and no more expensive than hiring digital backend work done, just drop the film in the post or at the lab and it comes back ready to show the client.
The basic thing film needs to be viable in a business plan is just a little time, just enough time to run through the lab after the shoot and get back before the sales appointment.
Wedding photography is conducive to this type of two appointment strategy, portrait work can also work well, anything in the fine art range of work too. A great historical example of this business model is Henri Cartier-Bresson.