I planted purple basil a couple of months ago; its true leaves were beginning to develop but a slug (I'm guessing) devoured all the leaves from the seedlings.
The stems are present so will it still be able to live and just regrow new leaves?
I am in California as well and had a nice basil plant growing in a pot in my courtyard where rabbits or squirrels won't be able to get in. I encountered the same thing as you where one fine day the entire basil plant was eaten up. It was the work of rats because I saw some rat poop in the courtyard. Sorry but basil seems to be very popular among rats. Who would have thought!
That will not regrow unfortunately. A plant grows by cells in a/the meristem (growing tip) dividing. If the growing tip of the plant had been left on the stem, then it could continue to grow, but in your case I think this is extremely unlikely. On most mature plants there are multiple meristems, which are usually found as buds on the stem, often where the leaves branch off. (Incidentally, this is how pruning works - removing the main growing tip encourages others to become active).