You still need humans to manage the whole lifecycle, including monitoring the live site, being on-call, handling incidents, triaging bugs, deploying fixes, supporting users and so on.

For greenfield development you don't need as many software engineers. Some developers (the top 10%) are still needed to guide AI and make architectural decisions, but the remaining 90% will work on the lifecycle management task mentioned above.

The productivity gains can be used to produce more software, and if you are able to sell the software you produce should result in a revenue boost. But if you produce more than you can sell then some people will be laid off.