Will development mode go away? Also can I use it for my site in production?

The development mode will stay free forever and you may use development mode on a production site. Development mode does not have access to the moderation dashboards but If this fits your use case, great! If later on you want to switch to a plan which enables moderation, that is great also and I can help you with that!

Summary: There is no pressure, you may use development mode for free as long as you like, but it lacks moderation dashboards.