only the front will cause issues with the front.
and yes, a track bar itself can go bad. usually that means it's damaged and/or bent. normally the bushings and tie-rod ends are the wear items. if we're talking about a stock OEM track bar, it's easier to replace the whole damn bar than try messing with the bushings or ends. they aren't that expensive.
if we're talking aftermarket, it depends on what you have and if its worth doing anything to. not all track bars are created equal, especially in the strength and clearance departments. many have horrible clearance, many use low quality parts, and many are thin walled tubing that's weaker than stock (stock is 1" solid bar).