you can go to the "cortex command" side of digging axpect of game (by that i'm saying less tiles/screen as possible) or a simplified digging game so you can wet you feet and feel if this gonna work or not.
i really dont kno how construct 2 can handle this kind of effect, but i remember quite well that someone posted a tutorial of terrain destruction with costruct classic using the mouse plugin and making a erase effect that look like it is deforming the terrain.
the first thing you need to focus is how to build the "simple" systems: terrain destruction, character movements, building system, types of tiles...
then you make the jump for the random terrain creation so you can experiment wich way is better for the gameplay and performance.
performance in this kind of games are very tricky, but if you really want to make a digging game using construct 2, try to build a very simple one first and then when the basic systems are done you can keep growing the game scale while keeping the good performance.
Eventually by the time your project hit the "playable" state, this performance issues will be easyer to solve, probably future features will be add on the construct 2 and maybe help you improve the game.