I would say at least 15 athletes at the moment could beat Webb in a 3000 race(all of the Major American 5000-10000 meter runners and basically all the nameable Africans on the current 1500-10,000 circuit). To say that Webb could beat a record like the 3000m record is completely absurd.
I doubt he could even beat the American record. Kenneisa Bekele couldn't even break 7:25 in his prime, what makes you think Webb can? He's well past his prime now, and what makes you think all of the following you have said above wouldn't apply to at least one of the current athletes that is better than him? If anyone has a chance, it's probably Tariku Bekele who is still very young and shown success at the 3000 distance or his brother, Kenneisa Bekele, for obvious reasons.
But hey, if he actually breaks the 3000 record I would be amazed. It's certainly possible, but it's also possible that the athletes currently much better than him could beat him to it. It's certainly a tough record.