I have a suspicion Roby's replacement might well be Lomax (if he gets through this injury relatively unscathed).
People are talking about him losing pace since the last knock. I don't think that's strictly true because Lomax was never quick in the first place.
When Johnny first cemented his place in the team it was primarily because of two extremely valuable attributes - acceleration and lateral agility. Even during his debut season he was regularly hauled down after lengthy breaks because his foot speed wasn't particularly great. But over the first twenty yards there were few who could lay a hand on him.
Since the injury he appears very heavy-footed - particularly changing direction. I fear like Tommy Martyn, whose main attacking weapon in his early twenties was an outrageous step off either foot, he has lost a certain degree of joint flexibility which might curtail his career at full back. Martyn could never perform anything like the kind of sideways shift by the age of 25/26.
From the outset I always figured Lomax would make a good hooker. He possesses all the attributes necessary. Whether after this injury he still has the goods we won't know for some time. But I doubt we'll see him as the last line of defence very often in the future.