As soon as your first Lemming touches the wide yellow brickwall at the right, utilize a Basher! You have no Blockers this time, so plenty of Lemmings will fall into the bottomless pit to the left, but you can't really do anything to prevent this. Once the wall has been broken thru, utilize a Climber, have him climb near the exit. Do not let him enter, instead, apply a Digger skill, then quickly a Builder skill to make him turn back from the exit. When he does just that, give him the Miner skill so he can build a tunnel to the fellow Lemmings stuck near the wide yellow wall. If your reactions were quick enough, your save percentage should be high enough that even with said casualties, you shall pass this level.