Hi Alexis,
When working with limited internet access you can still look up leads, create new leads and check in leads whilst working offline. Then once you get access synchronize the app and then both the leads in the app and your Marketo database will be updated.
Just a tip make sure you've got internet connection to login and event has been selcted before looking up leads, checking them in and creating them. Offline you cannot login and select events.
if you cannot use the Ipad app, then just keep two excel lists:
-attended
-not attended
then import the email addresses each into a static list, upload, then run a flow to update Member Status.
Alternatively, you could just go into the Member tab and update each person manually.
You should not allow anyone to import lists.