Will a national UK license be an EASA license after a hard Brexit? We'll know in 18 days.
No, we know now and have done for months. With or without a deal, from 1st January a UK issued licence is no longer an EASA licence. So will be no use for a job at Vistajet or any other European operator. Probably academic, since you also ned the right to live and work in Europe which 99.9% of Brits won't have.