Thanks for writing. Lilacs grow best from cuttings when treated with rooting hormone and potted in moist sand, perlite, vermiculite, or potting mix.
Happily, there still be hope for your lilac plant, as well: These shrubs often recover from damage to their branches by sending up new shoots from their roots.
I hope this helps. Good luck!
---Justin, Senior Garden Editor, BHG.com