How to migrate data from Google AppEngine Datastore

Roughly speaking, no.

The big demand of GAE is the integrated, scalable, cloud backend. Without the backend hardware, it's functionally Django on bigtables. If the customers (quite rightly) don't like vendor lockin, GAE is not for them.

What features of GAE would you keep, if not for the backend?

It sounds like you've got this entirely back to front and upside down. Typically changes are tracked using scripts, which you would then apply to the production database. I've never encountered a case where it made sense to import production data to the next version created from development.

If your database isn't currently in source control, the articles linked to from Jeff Atwood's article Get Your Database Under Version Control are a good introduction. Also, the free Redgate ebook SQL Server Team Based Development includes a chapter on source control for databases.

If you've been making changes via GUI tools and don't have any record of what's changed your best bet is a database comparison tool, like Redgate SQLCompare or Apex SQLDiff. These tools will generate the scripts to upgrade your production database to match the schema of development.

If the boss won't part with the cash for a comparison tool, you could reconcile the changes manually using a diff tool like WinMerge or DiffMerge. Use SSMS Generate Script tools to script objects to individual files, then use the diff tool to identify differences. Finally, hand craft the necessary ALTER statements for any changes to tables.