Orphaned users metadata is preserved when copying to Office 365. This capability relies on a Microsoft Office 365 API update and on a feature automatically enabled on the destination Office 365 tenant.
Sharegate version 5.8 or newer
Insane mode has to be configured prior to the copy. Only the Office 365 API supports this feature.
Any content copied through the normal SharePoint API will not feature the preserved users values and metadata. The insane mode limitations also applies to this feature.
Deleted SharePoint groups are not supported.