Lancers and Hold The Line Leader TC

Which takes precedence, a Lancer FLG re-roll, or the effect of the “Hold The Line Leader” Tactician Card that allows all flags to be ignored? My line of thought is that the FLG die should be re-rolled as (a) the re-roll is an integral part of the die roll phase and (b) thematically, it is the retreat effect that is being ignored, not the kill effect of long pointy sticks. Interested to hear other views or if there is a definitive answer that I have missed.

Yes, I agree with you: re-roll the flags but ignore all retreat results, original and re-rolled.

Exact,
a combat/battle is finished only, after including all "special rules like "Lancer-Rerolls"

And then the Hold the line can be played
"Play this card after opponent rolls his combat dice"