There are several ways this can play out.
I don't know if Jose Baez has filed for a speedy trial yet or not, but if so, the trial for the current three charges must happen within six months from the arrest date.
If that's the case, and prosecutors don't have enough to charge her with murder, then she'll just be tried on the child endangerment charges. If two years from now, Caylee's body surfaces, she won't be able to be prosecuted for murder, because that would be double jeopardy under Florida law (correct me if I'm wrong).
If Baez has not filed for a speedy trial, then that gives investigators and prosecutors more time to develop a case for murder and to develop the state's case against Casey. It also works to Baez' advantage, because it gives him more time to develop a defense.
Most defense lawyers in Florida whose clients are facing murder charges do NOT file for a speedy trial, because they want to have time to develop a thorough defense for their clients....UNLESS they file for the speedy trial just to call the prosecution's bluff.