As an experiment I tried taking a few cuttings from some basil that was dying. (the stems was woody)
To my surprise all 5 cuttings have the beginnings of roots. So my question is how developed do the roots have to be before putting them into soil?
If the basil has got roots, it is viable, so you can plant it in compost any time. You can also nip the tips out of the growing plants, thereby making them bush out, and root the tips in the same way. Be careful when planting though, having been rooted in water the roots are quite brittle, and if you're a bit heavy handed, you can snap the roots off in the planting process.
I have had difficulty in the past germinating basil - well not germinating exactly, but damping off once the seed has germinated. I do persevere with seedlings, but the nipping out the tips, and rooting in water, can keep you supplied with basil for the whole summer.
valmarg