I had an amber that I forgot about in my basement for over a year. I was cleaning out the basement one day and found it. The airlock was bone dry, but I figured "damn the torpedoes, full speed ahead". I bottled it without tasting, and after it had bottle conditioned for a few weeks I tried it.
It was good, flat, but good. To be honest, I hadn't brewed any during that year (it may have been my last at that point), so I think I might have forgotten to prime it. That would explain the flatness at least.
Anyway, my point is that leaving it on the cake for too long won't necessarily damage it.