Hello, I have also found that the data zeros out after an activity is no longer live, no matter the state.
However, the data does not disappear, it simply moves, much like if you were to change the name of an activity. See the difference below - 3&4 were where the data showed up while the activity was live and some time after it ended, it moved into 1&2 with the new "(deactivated)" name.

To make my dashboards more shelf stable, I've started using filters and segments for the experiences rather than pulling in the actual activity if that helps/makes sense.