Rollback to Previous Version

hi all,

I am sure this problem has been thought of before but I haven't found any
good solution to this yet.

Problem:
We release schema with versions 1.0.0.1, 1.0.0.2, 1.0.0.3 for example.

Now client installs version 1.0.0.1 in year the 2001 and then upgrades to
version 1.0.0.2 in year the 2004 and then to version 1.0.0.3 in the year
2005. Client is not satisfied in 6 months and now wants to go back to
version 1.0.0.2.

In these 6 months he has a lot of data logged and configured (new and
modified from version 1.0.0.2) in the current schema.

What are the different/best ways/practices of rolling back to the previous
schema version?
What are the best practices to save/log the data being deleted and schema
changes being made to rollback to previous schema version?
What happens if the client wants to rollback to version 1.0.0.1 instead of
1.0.0.2 from version 1.0.0.3?

thanks,
vish