While still with planets, the Saga of the seven suns from Kevin J. Anderson comes to mind that could be adapted.

Or some of the worlds from Warhammer 40K, specifically Fenris and some of the Maiden worlds lost to the Eye of Terror. Fenris would be great for a long term campaign with the time of Fire and time of Ice. For your vertical Land you could also use Fenris with the one stable mountain continent of Asaheim and the Fang, the tallest mountain in the Galaxy, so tall that its top pierces the Atmosphere and is a docking station for Spacecraft. Have the players be part of a out on the ocean and the time of fire nears, so they must forge a path towards Asaheim before all turns to oceans of boiling water and magma, with other tribes in the way. Sort of a RHoD scenario, but rather than the defenders you are the attackers this time round. With some effort and time you could add some elements form games such as FTL and this war of mine, making hard choices of maybe looting other tribes that are innocent or were once allies to try and make sure your own tribe survives.