Whatever happened to John J Sykes, in the 80's he was considered the Irish Eddie Van Halen. He left Thin Lizzy to make Whitesnake 87...after that I have no idea.
He formed Blue Murder and they released their great self-titled debut album in 1989 to moderate success.
Since then success has eluded him. The follow up BM album Nothing But Trouble in 1993 was good but flopped, as did his subsequent solo albums. I think he still records and tours as a solo act, mostly in Europe.
I think he is English not Irish. You may be confusing him with his Whitesnake replacement, Vivian Campbell (ex Dio now with Def Leppard ).