You don't need drug charges to be sentenced to a treatment program. Many theft
offenses are drug related, and it would appear that the state had reason to believe that drugs were behind your offense.
You got yourself a very nice deal -- case dismissed upon successful completion of your sentence
. All you had to do is complete the 90-day rehab and then stay out of trouble for the duration of your probation period. But by leaviing the facility without permission, if you are on probation, you'll be violated and, if you have already taken a plea of guilty, you can be resentenced to anything on up to the maximum amount of time for the charge to which you pled. You can expect that a warrant for your arrest has already issued when the rehab facility reported that you left.
So you are in very serious trouble. You will have to return on the warrant, get it vacated and then face the music. It is always better, in terms of penalty to do that sooner rather than later and voluntarily rather than after an arrest. You should reach out to your lawyer however, because you will need one with you when you return, as without one -- maybe even with one -- you are likely to immediately be put in jail, at least for a couple of days until the prosecutor gets his file and so that a new disposition can be negotiated.
I don't know why you left rehab, but you should share that with your lawyer, because you did take a plea to complete it, and courts
frown on those who take a plea knowing what the conditions are and who then turn around and say, "I don't think I should have to do this." You're going to need a better reason than, "I wasn't charged with drugs." If rehab agreed that you had no drug problem, that would be the only way that excuse would help you.
If you come in quickly and with a lawyer, he could make a pitch that you really didn't have much time to benefit from the sentence and to ask for another chance. If there's a legitimate problem with the rehab facility, then he can tell the court that too. If he is aggressive enough and can make a good argument about why you ran, if he can't get you a second chance, he can perhaps get you house arrest, since you never really had much of a chance for probation and rehab to "take."'
I know it's plenty scary. Situations like this are not pretty and there is no guaranteed good news for me to be able to give you. But you can make this even worse for yourself by burying your head in the sand and not coming in to deal with it. Come back quickly and like I have said, you still may be able to get another shot at a non-jail alternative.