If you’re a Ubuntu user, you may be familiar with ppa-purge. It’s a handy little automated script to remove a PPA and roll back the version of any apps installed from that PPA. Debian doesn’t have this nicety by default but there’s a relatively simple way to get something close.
Firstly, remove your PPA from /etc/apt/sources.list or from the /etc/apt/sources.list.d/ directory.
Do an update:
sudo apt-get update
Find any packages that are now obsolete:
aptitude search '?obsolete'
For me this returned the following:
# aptitude search '?obsolete' i A libmysqlclient18 - MySQL database client library i A mysql-client-5.5 - MySQL database client binaries i A mysql-server-5.5 - MySQL database server binaries and system database setup i A mysql-server-core-5.5 - MySQL database server binaries i A ruby-passenger - Rails and Rack support for Apache2 and Nginx
Now just remove the listed packages with apt-get remove and reinstall as necessary. It’s not quite the automated tool that ppa-purge is, but it’s a pretty good start.