Ok. This matter is a bit more complicated because you were on probation. So, in addition to this new charge, you will have to deal with a possible violation of your probation.
First, I'd like to discuss the new matter as a result of your driving. What it seems you are concerned with is a possible defense to your driving on a suspended/revoked ticket. Tennessee recognizes what is called "necessity" as an affirmative defense. Necessity is present when a criminal act is justified if it is immediately necessary to avoid imminent harm. Also, the imminent harm can not have been caused by you. T.C.A. § 39-11-609.
When it comes to invoking an affirmative defense, there must be a trial. This is because the jury or judge must determine if: a) the facts present indicate the possibility of an imminent harm and b) whether the Tennessee case law would also recognize your argument as valid under the law.
Furthermore, you, as the defendant, would bear the burden of proof in showing the necessity. In essence, an affirmative defense can be construed as "Yes, I committed the crime, but....". As you can see, these arguments are not always successful, but many are.
The fact that your friend, presumably, called you and he was in an a scenario where he would be severely injured, or worse, and you had no other ways to get him. There may be an argument.
However, these types of issues are very fact intensive, so I cannot say whether I believe there would be a successful argument. For instance, why didn't he call 911? Why didn't you call 911? Did you have anyone else who could have driven you or driven your friend? Where were you planning on going after getting to your friend?
These are all questions that need to be answered prior to addressing whether your driving can be excused. If you can respond to this post with those answers, I can better evaluate your ability to provide the defense.