His stores of Allomantic metals abruptly disappear. They're still physically there, but the power is completely gone. He immediately turns to go back, only to see more forest.
At least his Feruchemy still works—he can tell because he's still alive—but that won't last him forever. He only has so much stored youth, and without both sets of abilities he can't replenish it. He hasn't been in so much danger since the beheading that one time. Returning to Scadrial is the highest and currently only priority. If spontaneous forests are a thing, he needs to find someone who can explain them and more importantly how to get back.
The next few hours are spent walking in an essentially randomly chosen direction, with the sun to his right. He's quite certain that suns are supposed to be moving across the sky, but that's not a pressing emergency. He already knew he wasn't on his own planet when he saw proper trees and plants instead of ash-covered monstrosities. Whenever he calls out, nobody responds. If it's an empty spontaneous forest, he's probably doomed.
After some time, he hears his stomach growl. He hasn't seen much that looks edible, but possibly that's just because he's not used to real plants. Berries. Berries used to exist. Those berries look tasty, and if they're poisonous it's not like he needs to worry about it. As always, he has a truly ridiculous amount of stored health in his gold jewelry. Tapping gold just in case, he eats a handful.
The heavy thing knocks Alendi out of his trajectory. He falls a flight or two before catching himself on one of the landings, and decides there isn't much choice but to head back through the well and try to avoid heavy things.
The deafness doesn't help with avoiding them. Okay then, time to spend more resources than he can really afford to go straight up through the heavy thing-free ceiling.
He tries that.
The more important question is, how far across the atrium does he get?
He runs down the hallway and tries the third door on the right.
How about the second door to the right, does it have any objection to being battered down with a nonconductive heavy thing?
Acid's easier to dodge. And more likely to inconvenience any pursuers afterward. He keeps swinging. If this door can be broken by force, it will break soon.
That was to be expected. But if the magically sealed and acid-trapped door wasn't made immune to battering rams, the wall probably wasn't either. He turns left and tries bashing his way through.
The room Promise recommended is unoccupied, full of musical instruments, and possessed of the commodity of a balcony. From it, he can see the balcony to the Queenly bedroom. He cannot see the gate, because that is not how gates work.
On this balcony there lands a silver-skinned blue-eyed fairy...
"Cease," she commands sternly.
"No," he meets her eyes, "You stop."
While Alendi's looking over to see whether the smaller fairy's wibbling has intensified, he meets with yet another blunt impact.
He peels himself off the floor and directs the Queen, "Don't let anyone interfere with me." Then he rushes to grab her and jump for the gate.
And he's back in Scadrial, and Promise closes the gate and stares at the queen and trembles. (Yellow covers his eyes and squeaks.)
"I've told her to stop," Alendi says on the off chance that Promise isn't deaf right now, and gestures in case she is. "I...haven't really thought about what orders happen now."
"Can you hear?" she asks Alendi. "Make her forget my name, see if it works."
"Store Promise's name in this piece of copper," he says, holding an unused ring against her hand. "Nod when you've figured out how and done it."