The block that has separated currently from its brethren on the 3rd pitch of Quick Release would weigh in at 1000 lbs with total debris at dislodge being well over a ton. It vibrates with a four finger tap. It clearly blocks the center of pitch 3. You can climb another block that is pitching it on top. But my guess is, it would be a 50-50 proposition that if you weight the above block and then release, that would be all the momentum the loose block would need to find its freedom. The leader would perish. The rope cannot be diverted to avoid potential direct contact. The rope would no doubt be severed after the lead climber was pulled off. I do believe the belayer would survive however, to the east under a roof.
An accident happened like this on EEOR across the way last year, where a block did in fact terminate both the leader and the belayer.
The loose block on Quick Release is the most dangerous I have ever seen. Gravity has caused it to slide, flat surface on flat surface limestone from its parent. One small wedge stone, maybe weighing 100 lbs holds it in, but is also independent of its surroundings.
Quick Release, 5.10a, Ha Ling, Canmore, AB, August, 2008