I'm a software engineer that's lived through the dotcom crash and the great recession. I can tell you the dotcom crash was much more devastating for the tech community since we were at the center of it. There will always be a demand for software engineers, just keep in mind though that this demand is cyclical and during down years you have less leverage in salary negotiations and perks on the job tend to be taken away. If you are a good developer though you'll have little to worry about.