Thanks to Richard Cosner, it has been found that the game was infact completed and released.
SIR’86 did a loading picture which was done just to keep the publisher happy for the time being. It seems this was unused.
Case closed …
Contributions: SIR'86
Supporting content
Creator speaks
SIR'86 speaks about work on Eternal Dagger...
"Andromeda also contracted with SSI to do conversions of their adventure and strategy games to the ST and Amiga. Again these never got completed I did a loading screen for the game Eternal Dagger, based on the manual artwork, to keep the publsher happy.
It was only much later that I realised that the manual was sort of sepia / green coloured, but the actual box artwork was in full colour, so my picture's colours were completely off.
It's still a very nice picture though, and I still have it."
SIR'86.