In August I made a wedding cake which was marzipanned and covered in fondant icing. It was a spare so didn't get eaten and it occurs to me that it will be perfect for Christmas cake. It's been sitting in a cool, dry place since then (not frozen). I know the cake itself will be fine but what about the marzipan and icing, will it be edible? I'm guessing that it will just be very hard (which I'm fine with as it's probably just like royal icing then) but just want to check it will actually be safe to eat.
If it was sealed to a board, It should be fine to eat. At the worst, the colour from the marzipan will have leaked through. If it was open underneath, there is a chance that the cake has gone mouldy. Only slicing it will tell
It will be fine! - presumably a fair amount of alcohol went into the cake - the icing is just sugar - which is a preservative anyway so won't have gone off - as you say it may be a bit hard, but will be fine.
I still have a quarter of last year's Christmas cake and it is perfectly OK!