Game's save data file can be found in your device ( search Ixalon ) I haven't tried it with Eternum but did it with several other games , uninstalled the game but the save files seem to be secured in the device and whenever we download the game again , we can continue from where we left off ( and I dunno for any ongoing games I tried it for finished games )
I think you better get another copy of save data ( better not take any risks )