Ascension coming back confirmed???
Ascension is unlikely to come back in the form you're familiar with. If it's coming back, it'll come back on a different map. Currently, we've actually considered modifying the Nexus Blitz map for it (given how rounded the Nexus Blitz map is). If you notice the changes to terrain in the center "arena" area of Nexus Blitz, these changes are meant to help support much more interesting gameplay for other ways we can use that space. :)
The Crystal Scar is dead. Like so dead. Like omg dead.
The renderer for League's environment is completely different and new from what existed when Dominion (and so, Ascension) was made, meaning that a lot of what was made for that map is unusable and will need to be rebuilt. All the environments you see now were either built initially for the new renderer (Nexus Blitz or any of the TFT environments) or were rebuilt (SR, Howling Abyss). Keeping a map has to overcome the cost of that rebuild. :(