What happens after Mainnet?

Could you elaborate on what exactly transpires following the launch of a Mainnet? What are the key stages involved in the post-Mainnet era? Do projects typically undergo significant changes or does the focus shift towards other aspects of development? Additionally, how does the community and ecosystem react to the Mainnet launch? Are there any specific challenges or opportunities that arise post-Mainnet? I'm particularly interested in understanding the long-term implications of a Mainnet launch for a cryptocurrency project.