The common practice today is to build the new stadium in the parking lot and then demolish the old stadium for use as the parking lot, which is what happend in Cincinnati, Atlanta, Chicago, etc. Or to have a redevelopment plan ready to go, such as in Minneapolis. However some stadiums have lived on past the team leaving, generally because they were located in bad areas and the underlayig land was really not worth redevelopment. For example, Philly's Shibe Park/Connie Mack Stadium was left to just rot for nearly 8 years, because no one wanted the land it stood on. It is now a church.
I belive this is a list of the still existing abandoned major league stadiums.
San Francisco's Candlestick Park and San Diego's Jack Murphy Stadium are still used by the NFL.
Both Montreal Stadiums still exist, the intended to be temporary Jarry Park has been converted into a tennis stadium, and the "Big Owe" is still in use, although not for sports.
The Astrodome is sitting with no apparent use planned. Houston's original wooden and wood temporary Colts Stadium, was left to rot, but eventually sold, taken apart, and moved to Mexico, where it is still in use in the Mexican League.
While the original Busch Stadium (Sportsman Park) was torn down, the field remains and is used as a local children's park.
Two replicas of Crosley Field were built in the Kentucky suburbs, using materials from the original. The one in the gated community of Blue Ash is still there.
Boston's Braves Park was reworked as a football and soccer field and still exists, part of Boston U.
The LA Coliseum is still there, of course.
RFK / DC Stadium is still used by a soceer team, until 2010, and then there are no firm plans with what to do with the ultra-valuable piece of land. It is not even really clear who owns it. The DC government says it got it as a part of "home rule" in 1970, while the US government thinks it is still a part of the Interior Department, which built it and paid for it with federal dollars.
