It's definitely possible for chatGPT to replace all chat bots on Reddit, but it depends on the complexity and functionalities of each bot. Migrating from an old bot to chatGPT would require some retooling of your current codebase.
The first step would be to investigate the capabilities and limitations of chatGPT and to determine how to adjust your current bot's functionality to fit the chatGPT platform. Then it's a matter of reconfiguring your old code to work within chatGPT's framework.
Overall, it's certainly possible to migrate chat bots to chatGPT, but it will require some work on the part of the developer. If you're up for the challenge, it could definitely be worth it in the long run.