There's a handy FAQ section for Gemcraft: CS. I've copied/pasted the relevant bit for you below. You can find the full link here. Anyway, here's the part on missing save files:
It’s very important that you don’t create a NEW save game over where your old one was, if you do this it will overwrite your previous game even if it isn’t visible. Please log out of Armor Games, then log back into your account – 95% of the time this will fix the problem. If that doesn’t work, we suggest you reboot your machine.
If you used Local Save, it’s possible that clearing cache/cookies or your security programs may have deleted your game, and there is nothing we can do to help.
Most of the time when this happens, it's users losing their local saves because of cache clearing. Depending on the browser you're using, it might be automatically set up to clear the cache every few weeks or months. You can disable this in the browser's settings.
But, yeah, one it's gone--it's gone. There's nothing we can do to recover that lost save. At least you were only level 115, so that's not too hard to earn back. And it's a super fun game, so it wouldn't be too tedious of a process. Good luck!
