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That would be news to the Andromedeans - that their home galaxy has vanished!
Possible explanations:-
1) You were looking in the wrong place
2) You were looking at the wrong time (too low down?)
3) There was poor transparency with cloud, dust, smoke cover that you might not have realised was there.
4) Sky was too bright with light pollution and moonlight.
5) Your eyes were not sufficiently dark adapted.
Work on getting 1) and 2) right - M31 is a very easy target. It's at highest elevation around 10pm at the moment. Extend a line from Mirach (Beta Andromedae) through Mu Andromedae for the same distance and you are there.
With current Moon plus Sydney sky glow, I think you will have to work hard to pick up Andromeda, even with 10x50 binoculars and particularly if your eyes aren't dark adapted (try to get those street lights at your back and don't look at any lights for 20 min before you try to see it).
With less light pollution (at a location I visit some 50km from outskirts of Sydney) and dark adapted eyes, I have no trouble picking up M31 with 12x60 binoculars, even under full Moon!
Good luck!
ps, Go looking for NGC 253 in Sculptor - I think that is more impressive and still an easy binocular target.
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