Lufthansa cancelled my flights in April, I called them to rebook in June and they didn't charge me the fare difference on the new flights I wanted (which was around 300 USD) so I am very satisfied with the way they dealt with it especially as I got the initial flights for April for a very good price. Also never had to wait on the phone for longer than 10 mins! I still have another ticket to use, so hoping the experience will be the same whenever I get around to using it!