Workspace Reloader extension by Scott Hanselman preserves open documents in Visual Studio when a project is reloaded.

When a project in your current solution is changed, typically after an update from a source code repository, Visual Studio asks to reload the project:

Project modification outside the environment detected by Visual Studio

If you agree to reload the project, Visual Studio closes all open documents from this project. The Workspace Reloader extension reopens these documents as if nothing has happened.

The free Workspace Reloader extension supports Visual Studio 2010 and Visual Studio 11. You can download it from Visual Studio Gallery. Source code is available on github. Read about making of this extension on Scott’s blog.