Thats nearly right - the section of upper GI cut is joined back into the intestine just passed the bottom of the roux limb, this way gastric juices etc from the old stomach section can seep back into and through the intestine !
If you manage to pop open the staples (and it can happen) food or fluid would be allowed back into the main remaining stomach and you would find your able to consume more food in one sitting.
Any failure would require further corrective surgery.
Please dont be conserned though, i've read that its very rare for surgical revision to be needed, it can and does happen, but you'd need to really be abusing the bypass for this to happen, most people follow the rules and will never experience this, the studies i've read were about surgical failure in the US which was mainly due to the paitent continuing to heavily over eat post bypass.