How does PowerPanel implement legal obligations? For example, in Hostbill it is possible to delete invoices.
PowerPanel is a Dutch company so we are bound to the Dutch law. As for this example: it is not possible to delete invoices. You can, however, set them to zero.
Having all customer data in the cloud, how does PowerPanel deal with security?
Every credential that is stored is encrypted, every connection uses https, there are firewalls everywhere and many services work with IP whitelisting.
Is there a way to undo accidental edits?
You can simply choose the “undo” command (ctrl-z). If that does not work anymore, you can investigate the log files to see what was changed.