Sure, we should always think that. Russia's alliance with Armenia is not absolute. Russia wants Azerbaijan as well. They helped Azeris in 1920, 1921, 1923, and later in 1988-92. During the NK war, Russians were helping both sides, depending on their internal developments and momentary interests. We can never guess exactly what Russia's interests are at the moment.
As a general rule, if Armenia is defeated by Azerbaijan, it will lose its value for Russia. If Azerbaijan launches a surprise attack and quickly gains territories, Russia may threaten and stuff, but it will be too late, Azerbaijan will use the new gains to strengthen its position diplomatically (after all, de-jure, it all belongs to them), and again we will be presented with a new harsh reality (just like in 1916, or 1920). Russia will then start courting Azerbaijan i hopes of winning it over to its side. We will be royally screwed.
The only way to avoid it is to maintain the clear military edge over Azerbaijan. And with the oil money, it's a question if we can do that.