I asked this question on the Khador threads and people thought it worked one way but weren't 100%.
pIrusk's feat reads, "Feat: Undying Loyalty. While in Irusk's control area, friendly Faction warrior models/units gain Fearless, Tough, and +2 to melee and ranged attack rolls and cannot be knocked down. When a friendly Faction warrior model makes a Tough roll on a 4, 5, or 6 while in Irusk's control area, that model heals 1 damage point. Undying Loyalty lasts one round."
So if a friendly Faction multi-wound warrior model, such as a solo or a Man-of-War, rolls a 5 or a 6 on Tough, does the model heal 2? It does not explicitly say that the "heal 1 point" overrides Tough's old effect, merely that it triggers when a Tough roll is made. The people in the Khador thread that responded were fairly certain it was heal only 1 on a 4+, but I wasn't overly satisfied with the justification. The errata does not mention this scenario.
I am new to this game, but experienced at other games in general, so I would greatly appreciate a thorough explanation in addition to the ruling. Someone mentioned that two of the same named effects don't stack, but it wouldn't seem to me that the Undying Loyalty heal 1 on a Tough roll of a 4, 5, or 6 is an application of an effect named Tough, but an application of an effect named Undying Loyalty. If it were Magic, I could justify my interpretation with separation of statements by a period and calling it a triggered effect instead of a replacement effect, since a replacement effect would have used the word "instead". I'm not sure if this game's vocabulary is as well defined as Magic, as loosely defined as Warhammer or 40k, or somewhere in between.
Answers are very much appreciated!