wow, you're braver then I would have been in that situation. I was just thinking of score the inside with a glass cutter, or maybe drilling some holes near the edge, and then breaking it, and leaving the back/side still siliconed to the tank.
Good job though, that's pretty impressive.
I think the main reason the wire/line method didn't work is because it had too much area to cover, in addition to a bend.
all i had was the chisel and hammer or string. and i believe it was a mix of the bend and the angling i couldnt get a saw-like tension on the silicone and it got about 1mm and hour and that was not going to work. my heart dropped everytime i heard the cracking of the glass. but its totally gone and cleaned up now. tomorrow i put in a new moss wall and refill all fish look good still and hopefully becuase of the water drop my alfbnp start to breed if not oh well there all alive and well i cant ask for more