The rules for Trolls specify:
The Troll's Lair augments your region's defense by 1 (just as if you had an additional Troll token stationed there), and stays in the Region even after your Trolls go into Decline. Remove the Troll's Lair if you abandon the Region or when an enemy conquers it.
The rules for Hordes of tokens specify:
They disappear when you go In Decline, however.
Assume a Troll player goes In Decline, and one or two of their regions have a single Hordes of token, which disappears. Does the Troll's Lair remain? I have been assuming that it does. However, I just played a game on the computer where the Trolls went In Decline, the Horde token was removed, but the Troll's Lair remained behind with no race token in the region.
Looking at the rules, the region has not been abandoned, and has not been conquered. But this behavior seems unintuitive, and I suspect that it is an issue of an expansion (Small World Cursed!) creating an unintended consequence when combined with the literal text of the base game. It seems that in the base game, the Troll's Lair remains in the region because an In Decline Troll token remains in the region.
So, does the Troll's Lair token remain when the Hordes of token disappears?