How sure Microsoft will replace traditional addin dev method with SPfx? Where we can get the roadmap of SPfx?
Microsoft has no plans to remove the Add-in model if that is what you are asking. In terms of the SharePoint Framework, all indications are that Microsoft is committed to SPFx as the SharePoint development model moving forward. In my opinion, the big issue is the pace at which they are adding features that we can use. It's more than two years since they announced SharePoint Framework and all we have are web parts and extensions.
As to your last questions, you can find the roadmap here: SharePoint Framework roadmap