No, as they cannot make a normal move when within 3" of an enemy unit. As mentioned in 8.0 Movement, when within 3" of an enemy unit, you can only make a retreat.
25.5.1 "A Unit that has a conditional battlefield role keeps it for the entire battle, even if the conditions that required it to have that battleflied role in the first place change during the battle (your general is slain, for ecample.)"
Well, at least every Priest in the army can get a prayer. I think this one is clearer than Unique units and spells. As allied are not mentioned in the sidenote next to 27.3.1.
TL;DR: It is situational, just get another artefact.
The locus does not have to come from the artefact bearer. You could tie an enemy hero up with another hero, or prevent the enemy to pile into your "whatever" nearby unit.
Like using the Masque to tag Skarbrand so he can not pile into your Bladebringer shredding Blood Warriors.
Idolator Chaos Warshrines are, as mentioned above, no Heroes, BUT they are no longer Behemoth either. (Core Rules 25.5.1 Page 31)
Sorry, that only seems to work when the role is changed by the "Notes" column ..