If a feature slips and doesn't make it into this release, it simply goes into the next release. A consistent release cadence like this one works well if your team is doing Agile development and is either releasing after every sprint or combining every few sprints and releasing on a regular schedule.
Have a look at these two road maps to see the difference between a quarterly and yearly timed release road map.
When deciding on the cadence of a timed release product, take into account the rate at which your customers can integrate new products into how they work. For many corporate accounts, the process for accepting new software is slow and deliberate. They may not want to accept new or revised software any more than once a year. In the consumer market space, the cadence is much faster.
For example, Facebook updates its app every two weeks. In some instances your software is released to customers the moment that it's written and tested. This is called continuous deployment. Products using continuous deployment or those released more frequently than once a quarter still benefit from a road map. Product managers focus on creating themes that are developed over a quarter. You then have a road map which shows all the features that will have been developed by the end of a particular quarter. And your customers only get the full benefit of all the changes at the end of the quarter.