"the end is nigh" is a popular, but not very serious, way of saying 'the end is soon'. Nigh - nearly/soon (very old fashioned word).
Most popularly used to talk about the apocalypse, but pretty much always used in a joking manner.
"-ish" is a way of saying 'sort of' or 'a little'.
For example: "My painting was goodish" would mean 'my painting was a little bit good (but not 100% good)'.
Or, "lets meet at sixish!" meaning, "lets meet at around six".
So, this would mean "the end is sort of near". Again, more than likely as a joke.