If all members of a group delete their accounts, is all data, that was uploaded (not only personal data) deleted, or is it saved in the cloud? Who can have access to the data? Thanks for your support!
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Deleting an account only deletes the account. Confluence will put the users personal space in the bin, and all of the systems will throw away local personal information, but no, all the stuff you're trying to track, share, code for, and report on will be left intact. It'll just show that the authors are unknown or deleted.
The people who will still have access to the data are the people who had access before you delete the accounts and have not deleted.
No, the point of an issue tracker, documentation system and source code repositories (and the rest) is not to lose data.
Deleting a user's data just because they leave is the complete opposite of what Atlassian systems are for.
Data will only be deleted when you explicitly choose to kill it off.