It can be fixed, though you may need to buy a part.
Usually the handle is held in place with a cotter pin inside the valve body. It could be as simple as the cotter pin shearing off, or there might be something more complex going on. If you want to attempt the repair yourself, open up the main valve and look around to see what the handle connects to and if all of the visible parts are otherwise intact. The pump should be off when attempting this of course.