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 …
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."