What Happens when You Delete Accounts in Salesforce

User permission to delete Account : “Delete” on account object.

Most accounts and their associated records can be deleted in one click - but some accounts can’t be deleted until associations have been removed. This is not related from where you delete the Account: page layout, apex code, API, etc.

Deleted accounts are moved to the Recycle Bin, along with these associated items.

• Contacts
• Opportunities (if they're not Closed Won)
• Contracts (if they're not activated)
• Activities
• Notes
• Attachments
• Portal roles and groups (if all portal users in the account are disabled.)
• Partner relationships
• Relationship group members

If you restore an account from the Recycle Bin, any related items are also restored except for:

• Relationship group members in some cases. 
• Portal roles and groups. 

You can’t delete an account if:

• You don’t have the “Delete” permission on accounts
• You aren’t the account’s owner, above the account’s owner in the organization role hierarchy; or an administrator
• The account is enabled as a partner account; it has associated cases, activated contracts, or related opportunities that are owned by other users; or it has associated contacts that are enabled for the Self-Service portal.

If you attempt to delete an account that has closed/won opportunities owned by you, a message displays asking you whether you want to delete the closed/won opportunities along with the account or to cancel the account deletion.

Reference: Understanding What Happens when You Delete Accounts