Is there any draining system in the pot? If not, then over watering might have done the harm. Whatever it is we will never know. Also I would like to ask the age of your plant. Tulsi can die anytime between 1.5 years to 3 years. At least in my place I have seen so, but obviously after flowering and producing seeds.
Now, coming back to your question, are the remaining leaves still green or are they turning brown? From your picture it can't be understood if the petiole of the leaves are still somewhat strong. To be sure if your plant if still alive or not, sharply cut a stem and scratch it with something pointed. If it is green inside, chances are your plant is still alive.
If it is still alive, you can try re-producing it by planting a stem from it. Though I have not tried this method but all these sites suggest you can do so, provided if your plant is still alive.
Follow all the procedures mentioned in those sites like drainage system, sun light, pruning and it is likely that it will re-grow.
If your plant is dead already, I am afraid you will have to collect Tulsi seeds and plant them. More information is here.