Sessions created using New-CimSession persist until the CIM session is removed (by Remove-CimSession) or the PowerShell session ends:

PS> Get-CimSession | Select-Object Id, ComputerName, Protocol
Id   ComputerName Protocol
--   ------------ --------
 1   CIMTEST      WSMAN
 2   localhost    DCOM
 3   CIMTEST      DCOM