The FMC will calculate a direct route between the last waypoint of the STAR and the IAF. The question is, to connect those points or not?
Not a 767 pilot but IMO No. If you're not cleared that way, don't remove the disco. Don't set yourself up for a fall. By leaving the disco in, at least the aircraft will keep going as per the last clearance and if all else fails ie you don't get a Heading from ATC, you will notice the roll mode drop into Heading and you can then quiz ATC.