I'm a member of the IBM RFE team - data architect.
As a downstream data consumer of AHA REST API data I don't know when ideas have been deleted. There is no active 'this idea has been deleted' indicator.
Therefore, in my downstream data I have to cycle through ALL ideas regularly to test if an idea is still there.....then I FLAG it is deleted in the downstream data.
I suggest you either 'flag' ideas as deleted, and put a parameter in the API to show_deleted=true,
or have a separate API to list deleted ideas....perhaps keep them for 30 days or whatever.