Oh my, I saw him in 1976 with Rainbow - my first rock gig coming back from Zaire (where Rainbow didn't tour!), he was a young man then ...
The hits are getting closer day by day ...
I once read in a Dio interview that he had severe drug issues in the 80ies which eventually saw him fired from Dio. He might have paid a price for that.
As for his playing with ze Scörps, I'm with the "demo only"-theory: What ended up on the Love at first Sting-released version, had Francis Buchholz written all over it, a very engineered, clean, economic and dare I say Teutonic style, Bain was much looser and raunchier in his style, he must have totally disowned his style and copied Francis if that is him on that album. The drums don't sound like Rondinelli either, but very much Hermann ze Tshörman. Bain and Rondinelli were slated to join the Scorps, but Rudolf Schenker was as always concerned about "ze feeling being right in ze band", so Hermann and Francis were allowed to return after they had cleaned up their act from alcohol (Hermann) and personal difficulties had been overcome (Francis). Dieter Dierks, the Scorpions producer, was also supposed to have issues with the (German) Scorpions rhythm section at the time, he was looking to Def Leppardize the sound of his protegees, Mutt Lange's work impressed him hugely.