Gmaxwell and others have been advising against brainwallets for a reason... they are not and will never be safe. Just get bitcoin core and backup your wallet.dat, it's the best way to go to avoid weird shit from happening.

I guess electrum is safe if you like that route, but i feel safer with core. Also worrying about this thing is like worrying about the chances of a big asteroid hitting earth and destroying it... it can happen, but the chances are so slow that it's better to not think about it to avoid unnecessary stress.