... without it for a ride?
One of the legs had somehow been rubbing against the disc and had gotten worn. I suspect its only there to keep the pads in place when the disc has been removed. Will I get away with a ride without the pads falling out?
In my experience 'Yes'. I've ridden 7 days around Wales this last week plus 3-4 events in the previous month, all without a spreader on the rear. It must have a purpose but I don't know what it is.
To help the pads retract with the pistons. Worse that will happen is you'll have the pads rubbing all the time (which as a Juicy 7 owner you're probably used to). Why not just go and buy some new pads, if the spring wore down it is likely the pads need replacing anyway and you get a new spring with the new pads.