I cannot imagine how a Turkish invasion of Armenia would not precipitate a Russian intervention on Armenia's behalf. This could very easily spread into a broader war, or perhaps not if the rest of NATO views this as a war of Turkey's choice.
Armenia strikes me as being nearly indefensible, if attacked from the west while it is waging war in the east. Its only hope would be to last long enough against Turkey for Russia to be able to bring its forces to bear against its western neighbour. Can it? I wonder.