It's not a "non-need", but it's not the end of the world, for several reasons.
First off, everything comes down to time. If one had, say a decade, they could build a full, brand new gas production infrastructure from scratch, designed to produce in different parts of the world and export straight to the EU.
Great, except EU gas reserves aren't that big. They have a max capacity of about 6 months, usually filled to about half that at this time of year, though higher than average now. Russia makes up 30% of EU imports. Basically, reserves provides something like 9-12 months of Russian cutoff.
Next we have instant displacement. Much of the EU has been working to shut down coal power plants, and ones that are in operation are often run at lower and lower capacity factors. In the event of a full Russian gas cutoff, these would be all fired up and used heavily, while NG plants would instead be mostly shut down.
Then we have slower displacement, which can take anywhere from a month or so to a couple years. NG power plants can be converted to other thermal sources. Industrial consumers of NG for heat can switch to other heat sources. Etc.
On the home and commercial perspective, the higher cost of gas will lead to more investment in efficiency on its own. Government efficiency programs can improve this even further.
On the production side, the spike in gas prices will instantly make higher-cost, formerly unecomomical European fields economical. Some of these will be available right away, some will require weeks, some months, some years to bring online. But it does put a lot of new gas into the picture.
On the non-European side, there's LNG. The US is really a read herring on this front, at least for the time being, as Sabine Pass won't come online until the winter after next, and others even later. The Middle East is the primary LNG exporter here, particularly Qatar, whose LNG capacity alone is more than all the gas Russia sells Europe. Thankully, the EU is loaded with largely idle LNG import terminals (nearly enough to replace all of Russian gas as-is), and LNG tanker rates are very low right now, there's a glut. Now, Europe would have to pay a very high price for it. LNG is expensive to begin with, and they'll be competing with the gas's current customers, primarily Asia. Europe, of course, would pay more, leading to all of the aforementioned things - increased production, increased displacement, etc - to occur in Asia to offset their reduced LNG imports. Interestingly, the US actually *can* help there - the US does have a Pacific LNG export terminal that was recently brought back into operation at Kenai, Alaska.
The net combination of these factors is that, no, Europe will not just "run out of gas and freeze to death" or any of those other doomsday scenarios that people throw around. But there's no question that Europe will have to pay more for gas, probably at least 50% more. And nobody's going to like the resumed usage of coal power - but in the short term, they're not going to have a choice.
On the other hand... for the EU, the extra energy costs for gas and oil may represent something like a 5-10% GDP hit. But for Russia, losing all of their oil and gas exports would be like dropping a nuclear bomb onto their economy.
