Just one correction to your otherwise spot-on description of Kingsley....it was actually Macendale that paid the Foreigner to kill Ned Leeds. The Kingpin provided info to both Spider-Man and Macendale that Leeds was the Hobgoblin.
The aftermath of Leeds' murder is shown in Spider-Man Versus Wolverine (with not clear explanation given...it is assumed that Leeds was getting to close to his investigation of Russian mob activity). A few months later in Amazing Spider-Man #289, we are shown the meeting of Macendale and the Foreigner and the actual account of Leeds' murder. Interestingly though, in the first account Leeds is tied to a chair in civilian clothes. In the flashback he actually fights the killers in his Hobgoblin gear....probable mis-communication of the creative teams of the time or as I've always thought...Peter David wanted to explain an un-needed murder of a long-time supporting cast member. Remember, David only wrote that one issue of ASM, and there was nothing concrete to point to Leeds being the only or even one of the Hobgoblins at that time. And, for many years after, we are led to believe that Leeds was the one and only Hobgoblin.
I was 9 to 13 for the original Hobgoblin story (ASM #'s 238 to 289 with tie-in's)...this was all the talk of Marvel fans in my area at the time. I still think any version of Hobby beats out any other Spidey villain!!
If memory serves Kingsley revealed in Hobgoblin Lives that he knew the attack was coming thanks to his own intelligence sources and that he fooled Macendale and everyone else.
The death of Leeds as Hobgoblin was a hastily written mess that should not have happened, but Stern didn't get to unmask his creation before leaving the book and as I recall, editorial at the time did not agree with him that Kingsley was indeed the Hobgoblin.
Kingsley returned because Macendale became an embarrassment to the name Hobgoblin that he, Kingsley, had created and disposed of Macendale.