Height limit for building is 128 blocks

have your freind join the game. let them walk into the nether and teleport to them.

Use flint and steel to die

Then they'd lose all their items. And keepinventory disables achievements because it counts as a cheat option in bedrock

But all you said was that you had a flint and steel and obsidian. Even if it means losing the items it’s better than losing the world

I mean
True