Very mixed feelings if we were to let Field go and replace with Croft.
As stated above, i think very unlikely French or Field will get attractive offers to go back to NRL due to their size. Croft is more likely to go back at some point - so probably lose him sooner than later. Overall he's probably a more rounded 6 than anyone else, but I think French is building onto the role and getting better every game - just like Smithies is developing how ball playing skills. (as an aside I'm not sure the coaching team are getting any credit for developing the players skillset that we can all see in front of us - the inexperienced coaching team must be doing something right.....)
I think people forget Field is still coming back from a 2nd major hamstring issue too - I think he's still holding himself back and not really stretching out his legs and trying for full speed. I think we're gradually seeing more of it as the season goes on - latest HKR game being an example and i think we'll see more as we get to the end of the season. He is still playing much more of a link full back role though - and doing it well but could provide more threat running.
At the moment he has to make the gap himself and get on the outside shoulder of a lazy defender, against good defences less likely to happen - but if the coaching staff are able to get KPP, Dupree Nsemba or even Smithies working on a short pass or offload I think we'll really see the x factor that he brings. If we can work that out I'd rather keep French and Field long term.