If he can't find you, he can't subpoena you. If you are not interested in cooperating, just sit back and do nothing. It is not that easy to subpoena someone in a different state. There are procedures that have to be followed. If you are willing to testify, you should contact the DA and let him know about your travel restrictions. Depending on how important your testimony is, he may be able to postpone the trial to accommodate you.
The DA could certainly try to subpoena you. Because you live in a different state, however, the DA doesn't have jurisdiction over you or the authority to issue a subpoena. The DA would have to contact the local DA in the jurisdiction where you currently are and have a superior court judge in your jurisdiction "so order" a subpoena and then it would have to be properly served on you. This is no easy task. depending on how important the case is they may or may not pursue it. If you are personally served with any legal paperwork you should speak to an attorney ASAP to determine what, if any, your options might be. Failure to comply with a proper subpoena can lead to you being held in contempt of court.