Amplified nether amplifies world height to 255 and this means if player gets on the roof he can't build portal and get back. He stuck on the roof. He can't even die. As a creator of 1m downloads modpack I'm a greatly annoyed on this problem because of many complaints. What's why I written this script.
Lastest version: #1140091850422763581 message
#Amplified nether and players stuck on the roof.
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Paste version of nether_roof_fix.js from @gritty sinew
"suck_on_nether_roof"
ohh. stuck
Amplified nether and players stuck on the roof.
Paste version of nether_roof_fix.js from @gritty sinew
If i had this issue, i'd make the player take wither damage if he's in the nether above Y256

Then it will remove the vanilla mechanics of moving on the roof of nether. Players will not be able to pick up their loot from there.
suits them for moving above the nether on an amplified world 
could also teleport the player 10 blocks down, and break every "natural" nether block (netherrack, basalt etc) in 3x3 around the new playerposition
I already have this mechanics(a little bit more complicated) but if player fells out of world. ))))
I thought about what but I don't want to prevent access to nether roof.
Paste version of message.js from @gritty sinew
It telepots to 245 and while player take in block damage teleports him down.
If he trasfered this way from 245 to -60(no air), it creates cube 3x3x3 on 245 and telports player to it.
interesting
Full script
Paste version of end_fix.js from @gritty sinew

Full feature list:
If a player enters the end for the first time, but another player has killed a dragon, another one will be revived for this player.
If the player tries to leave the dragon island without killing him, he will be teleported back to the island.
If the player did not collect the eyes from endrem on his own, then he will not be able to get into the end.
If the player jumps into the void, he will be returned to overworld.
If he does this during the dragon's rebirth, the rebirth will be canceled and the player will not lose the ability to automatically revive the dragon.
And no, there's not even half of it. I supplemented it a lot.