I'm not one of those to count Nate out entirely, but he is coming in with absolutely no fight camp, and he's been hit or miss in the past.
That said, assuming Nate DOES beat Conor:
Option 1) Conor goes back to FW. Defend the belt. Easy call is that Frankie gets the next fight with him.
Option 2) If Conor is done with the FW weight cut, he can try to stay at LW. Declare that he wants to take a run at the LW division now, and that he just needs to make some adjustments to adapt to LW or whatever. It's not a tough sell, but it won't make sense for him to get an immediate fight with RDA. More likely he rematches Nate, maybe gets another 10 Top LW tuneup fight before another crack at an RDA fight.