First climbing session after the coronavirus lockdown. Both climbers familiar with the quarry (and observing social distancing). This was the third route of the afternoon, we were warmed up and happy with the standard we were both climbing at. The route "Elbowed Out" was chosen because we both felt it was within grade, and I had climbed the route before. I knew the route was a bit loose at the top, so I belayed off to the RHS to avoid any falling debris. Once my partner had clipped the third bolt, and as he pulled on a hold, a central part of the crack system broke away from the wall. The main falling mass was approximately 0.5m x 0.5m x 1.0m. He shouted, and as the rock fell I ran further to the RHS to get clear. In doing so I tripped, stumbled and released the dead rope. Fortunately the climber wasn't relying on the falling rock for support, and had grabbed a quickdraw as the rock broke away, so remained on the wall. As soon as I could I caught the dead rope again and called up to my partner to make sure he was ok. Once we were happy we were both fine, he made himself by safe clipping his rope loop to the closest (third) bolt using four quickdraws (two pairs clipped in parallel, with each pair opposing). While he did this I realised the rope had suffered major damage, leaving the core partially severed - roughly 1/3 of the core was intact. We talked through and agreed a plan: - First I tied-off the belay device, and made myself and the rope safe from further damage by moving out of the path of any more falling rock (down to the LHS of the route). As I did so I grabbed his rope and belay device. - He then used a screwgate and his cow's tail sling to attach himself to the second bolt, giving him a backup (although a very non-ideal backup) anchor. [Failure of the top anchor (third bolt) would have resulted in a 2-metre Factor 2 fall on a dyneema sling on the second bolt. Really not ideal, but we felt it was justified because a poor backup is better than no backup.] - I then had him double-check his gear, to make sure he was safely anchored to the wall by two separate systems. - We were afraid of lowering him on a damaged rope, so I attached his undamaged rope (plus a spare screwgate) to the damaged one. He then pulled up both ropes. I kept him on belay as he pulled the ropes up, but there was little point in this - there was enough slack paid out for him to reach the ground if his anchors failed. - He tied-in to the undamaged rope, and secured it to the third bolt (getting a bit crowded up there on bolt #3) with the screwgate. I then swapped the ropes on the belay device. - He disassembled his anchor system, and I lowered him down off the screwgate on bolt #3, and a snapgate on bolt #2 (as a backup).