If only you could figure that out ahead of time. I've been on projects that were killed with no notice anyone could see even in hindsight. I've been on important projects that senior leaders decided to out source my job to China and my boss was forced to let me go. I've seen budgets run dry many times and important projects got killed/cut with no notice (sometimes there are signs that but you think your project is important enough to escape the cuts until it isn't). Sometimes you are doing working everyone tells you is critical the day before they show you out the door.

I've also seen people make careers out of taking over projects cut for the above reasons as customers still demand support. I've seen many downturns where my project was important enough to not be cut.

I've seen many downturns where my project had massive cuts, but I personally was not the person cut. Most often projects are not killed outright, instead they go through a long down spiral (not always, but typically) and you can make a lot of money being the expert on a product that is making money if you are able to hang on. Someone needs to leave as there isn't the budget to pay everyone, but that someone need not be you. Often these projects pay very nicely for working 9-5 with no pressure to do overtime.