Bale scored an insurance goal in the 84th minute, with help from Karius.
Dani Carvajal could also be seen sobbing uncontrollably, his face buried into the turf as his night ended prematurely.
Salah tried to continue but had to be substituted in the 30th minute and Liverpool's 44-goal top scorer was in tears as he left the field. There was no doubt, however, which injury threatened to have the more serious consequences.
But although the loss of Salah was undoubtedly huge, Sadio Mane and Roberto Firmino caused Real problems in the second half, with Mane scoring a 55th-minute equaliser four minutes after Benzema's opener.
Salah got caught in a tangle with Real Madrid defender Sergio Ramos and as the two fell to the ground, the Liverpool winger's shoulder came under the Los Blancos' defender's body and immediately he signalled for the physio.
After collecting a through ball from Toni Kroos, Karius attempted to throw the ball out only for Benzema to stretch a leg out and poke the ball home.
Real thought they had taken the lead just before half-time when Benzema, preferred to Bale, turned in from close range after Ronaldo's header was parried by Karius - but an offside flag cut short the celebrations.
Karius' nightmare continued when he fumbled another Bale drive into the net for Real's third goal in the 83rd minute.
Dortmund made a ideal start, with Pierre-Emerick Aubameyang giving them the lead just five minutes in, but Wolfsburg produced an emphatic response, scoring three goals in 16 first-half minutes.
Yet Bale was clearly emboldened by his first goal and when he let fly again from 40 yards the ball swerved in front of Karius and went straight through the goalkeeper's hands. Madrid might have added more in the final exchanges and there was an incredible moment when Ronaldo was about to shoot only to be interrupted by a pitch invader.