Essential oil extraction using ethanol
The primary compounds of potential theraputic interest are all far less volatile than ethanol.  Ethanol based tinctures are sold and even have   available MSDS, so at least some of the oils of interest are soluble.  In looking at the chemical structures of the predominant oils of nigella sativa I would guess that they should all be fairly soluble in ethanol.  In some ways it seems that pure acetone (available at pharmacy) might make a better solvent and is even much more volatile even than ethanol.  If you used acetone, be certain to dry it via heating and time such that there is no scent of acetone remaining.  This shouldn't be difficult.  

Anyway, to answer your question: ethanol should be a good solvent and it should not be difficult to remove the majority of the ethanol from the far less volatile oils just by drying in air for sufficient time (until you don't smell alcohol).