Muska survived the end of the filmEveryone seems to assume he fell to his Disney Death even though it wasn't shown (and the film wasn't shy about showing some serious falls). Sheeta and Pazu manage to cling to the roots, the number of roots there and the close proximity between the three of them makes it more than likely he could to the same. Plus it would just be super poetic for him to survive and be trapped in the very place he had spent his life searching for, while deprived of its technologies and not even having working eyes to appreciate its beauty.
- The tree (with the remnants of Laputa still attached) rises into low orbit by the end credits. Muska has no way to provide for himself or navigate, and there's no telling if the tree is still low enough for the air to be breathable (small animals can be remarkably hardy in this manner). If he didn't fall to his death, he's going to suffocate or starve.
- He could find some stuff the soldiers left behind, build an parashute from it and simply jump.
Dola is Pippi Longstocking grown up.Think about it. She's super strong, super awesome and a pirate. And there is a picture in her private chambers on the Tiger Moth that looks suspiciously like early Pippi Longstocking concept art that Studio Ghibli did when they wanted to make a Pippi movie.
The siege Laputa made on the earth is similar to the war the Journey characters waged with each other, which ultimately destroyed their civilization.The cloaked figures in Journey fought against each other to gain absolute control of the destructive energy source they'd discovered. The Laputians destroyed parts of the earth before they learned that life and compassion, not power and destruction, are the most important things. But, as both universes learn, having ultimate power without the wisdom and compassion to understand it will just destroy and cause tragedy. In Laputa the world got off easy, as the Laputians learned their lesson before destroying everything, unlike in Journey.