Explanation
The likely cause for why a rehired user is no longer able to access records they worked on before leaving the company is that the records were manually shared with the user. Manual sharing allows granting access to individual records to specific users or groups. However, manual sharing is removed when a record owner changes or when a user's role changes. When a user is deactivated, their role is removed and any manual sharing involving that user is deleted. When a user is reactivated, their role is restored but manual sharing is not. Therefore, the rehired user will not have access to records that were manually shared with them before deactivation. The stage of Opportunity records, permission sets, or record type of Opportunity records are not likely causes for why a rehired user is no longer able to access records they worked on before leaving the company. References: https://help.salesforce.com/s/articleView?id=sf.sharing_manual.htm&type=5

Explanation
Web-to-Case and Email-to-Case are two solutions that allow customers to create cases from a web form or an email. Web-to-Case generates HTML code for a web form that you can place on your website. Email-to-Case converts incoming emails into cases.
References: https://help.salesforce.com/s/articleView?id=sf.customizesupport_web_to_case.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.customizesupport_email_to_case.htm&type=5