They've already begun replacing them in my area with Ford's replacement Interceptors based on the Taurus and Explorer chassis. I've done some reading on them and Ford really went to town specializing them for police duty with beefed up suspension, integrated roll cage, ballistic panels in the doors and run flat tires. They are factory equipped with provisions for lighting packages too. According to their data the all wheel drive Taurus will go 148mph! It's faster in both acceleration and top speed than the Crown Vic ever thought of being. Our Sheriff's Dept. has bought quite a few of each.
They also have bought a number of Dodge Chargers and believe it or not they are equipped with V6 engines. The cost is $1800 less than the V8 model so that's the route they went. I'm curious to see how well all of these hold up under severe service for the life of the car. They are running them around here to 150,000 miles before they turn them over.
The State Police are experimenting with the Chevy Caprice, Ford Taurus and Dodge Charger. I've yet to see an Explorer in NYSP trim. Both departments have a number of Chevy Tahoes.
The Crown Vic sales had dropped off so much that Ford withdrew them from the retail market in 2008, only fleet sales to police and taxi agencies were offered after that. I guess that wasn't enough to keep them viable, and from what I've read the Taurus is a much better car. I'm still interested to see how they hold up compared to the Crown Vic.