First of all : "Never" use Employee Domain Accounts to be used as Service Accounts for any application, let alone SharePoint.
You should look into these following articles from Technet that explains the correct practice to do so.
Plan for Service Accounts - SharePoint 2010
Said so, there is a way to take over the farm once again using the following approach in the right sequence :-
- Create a Service Account in the Active Directory and for now do not enable any password expiry policy. You might want to add replication rights incase you have used User Profile Service Application in the farm.
- Add the service account user as local administrator on all the servers in the farm.
- Login to the SQL Server where your SharePoint Configuration and Content Databases reside with "sa". Add a new SQL Login for the SharePoint Service Account with db_creator and securityadmin role and map the service account as dbo for all the SharePoint Databases.
- Now login to any one of the web servers with the local administrator. Try to open Central Admin. Chances are if you havent removed the default BUILTIN Administrators from the farm administrators group , the central administration site will open to the local system administrator with full access to the farm.
- Add your new SharePoint Account as the farm administrator through the Central Admin.
- Configure all farm services (central admin , owstimer and trace host) to run on the context of this service account.
- Validate the entire activity.