Roberts to right wing and Charnley to centre seems favourite. Josh played 3 when on loan at HKR.
Joel returning as right sided 2nd row with Hock replacing Hoffman as left sided 2nd row. That's if either are good enough to keep HH out of the starting line up.
Mellor appears best bet to 7 should Deacs retire. Not played first team rugby yet but he would be surrounded by experienced players in Lockers, Finch, Tommy, etc. Mellor would learn an awful lot from those guys.
Having gone through all that, if an International top class centre became available and was prepared to come to Wigan then I'm sure IL & SW would bring him in.