Hi,
I´m not Ian but I can also answer this 
… When your subscription ends, you have no further access to the charts - you can still use the chart-app in demo-mode, which only contains two sample airports to show new customer the functionality and the features.
The reason is, that the charts will also (in the same sync cycle as the data) be updated automatically every 28-days - and we don´t offer any outdated/old charts nor data. Sorry.
Hope that answered your question …
Cheers,
Richard