Q: If the AI spider bot needed a soul to re-energize, what would have happened if the Beast had done it first?
In the activation scene, we see the beast about to put the talisman in it's slot. He stops when he hears 9 and 5 trying to free 2.
In the following scene after 7 beheads the beast. 9 puts the talisman in and it activates, sucking 2's soul up. Then the AI spider bots activates from underneath the flag.
If the Beast would have plugged the talisman into the Machine Brain then it would have been re-activated and resumed hunting for its prey.
Since humans have been wiped out then it would engage anything it perceived as a threat or as a resource. The Beast was created by the Machine Brain so like all of its creations it would have worked for the Machine Brain and answered to it.
If 2, 5, 7 or 9 happened to be around then they'd become prey for the Machine Brain.
So no difference. Doesn't matter who plugs in the power source into the Machine Brain.
The real question should be: what does consuming souls do for the Machine Brain?
-"But you know what's on my mind right now? It AIN'T the coffee in my kitchen..."