I've recently ordered lavender young plants (4-5 cm tall) and it took then long time to arrive as a result most of the leaves decayed only leaving them with stems and roots (roots are in good condition) and some of them have been left only with roots.
Question
Is there a chance to revive the young plants after such stress or regrow them from roots only?
In theory, no; lavenders don't regenerate from basal wood, but that's on old plants - sometimes, in young plants, they do. If the stems that held the leaves are still live they should put out new leaves, but if they've been killed right back to the root, its not likely you will get new growth from the roots.
They should really be returned to the supplier, but if that's too difficult, pot them up, water and leave in a reasonably sunny place, outdoors if your temperatures are good, under cover or inside if not, to see what happens.
If you can "take them back" then that seems like a fine solution.
If you can't or prefer not to take them back, it seems likely the plant will come back. Layering and cutting are commonly used propagation methods so it should be possible to get them to grow if there is some portion of the plant that is alive.
If you post a picture it should be possible to give better advice.
