Establish what actually happened
Record the account type, deletion date, actions taken and any later migration, licence change or reuse. The words deleted and recovered are often used imprecisely. A message located in a recipient's mailbox is a surviving copy; that is different from recovering an item from a deleted structure.
Settings control survival
Exchange Online has Recoverable Items mechanisms whose behaviour depends on configuration and applicable preservation arrangements. Google Vault retention and holds apply within supported Workspace conditions. These enterprise features should not be assumed to exist for consumer accounts. Verify the relevant settings and history for the actual account instead of applying a generic retention period.
Preserve what remains
Identify current mailboxes, archives, exports, backups, endpoints and other authorised custodians. Necessary account protection may have to proceed while preservation is arranged; record changes and coordinate with the responsible team. Avoid treating a successful search as proof that all relevant data was preserved. Feasibility should state which sources can be examined now, which history is uncertain, and which losses cannot be remedied through the proposed method.
Sources & further reading
Primary references support the technical explanation. They do not establish D3 validation of a particular method.