Do temporary hit points from the Heroism spell keep a troll alive?

Question

The Troll's Regeneration feature states:

The troll regains 10 hit points at the start of its turn. If the troll takes acid or fire damage, this trait doesn't function at the start of the troll's next turn. The troll dies only if it starts its turn with 0 hit points and doesn't regenerate.

Let's assume heroism has been cast on the Troll, a spell which states:

[...] Until the spell ends, the creature is immune to being frightened and gains temporary hit points equal to your spellcasting ability modifier at the start of each of its turns [...]

Let's also assume the troll has taken acid/fire damage, and is at 0 HP. What happens at the start of its turn?

Answer 1

Temp HP can't save the troll (or anyone else) from the consequences of having 0 hit points.

The rules are clear that temporary hit points aren't "real":

Temporary hit points aren't actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.

[...]

If you have 0 hit points, receiving temporary hit points doesn't restore you to consciousness or stabilize you. They can still absorb damage directed at you while you're in that state, but only true healing can save you.

No matter how many temporary hit points the troll has, it still starts its turn with 0 actual hit points and does not regenerate, which means it dies. Just like a PC with 0 hit points and 10 temp HP still rolls death saving throws, and can still die if they fail 3 of them.