I would take the position that, although the Versys (and most modern bikes) are fairly bulletproof, you do not know how well it was treated in the first 600 miles. Neither does the dealer. They can argue it was well-treated, but if it was a demo bike, it was ridden by prospective customers and likely was not ridden as carefully as you would have ridden it as your own. That is a negotiating point.
Also consider that the dealer prep/freight charge no longer applies, so if someone bought a new Versys for, say, $6700 out the door, take off $200-300.
I bought mine for $6050 (not including $250 prep/freight charge and tax/title) from a dealer that wanted simply to be rid of the bike. If they are willing to effectively negate any profit, I would guess that a demo should cost no more than that, probably less.
If it were me, I would pay a fair price but try to get some accessories into the deal (free screen, bags at cost and installed), free service, or possibly a free extended warranty. It is very easy for shops to absorb labor costs into a deal, so maybe free lifetime oil changes or a free set of tires and a battery would work. I know that some dealers are okay with making no profit on accessories if it moves a bike out. I do most of my own service, so accessories would be a priority rather than service or warranty.
I think they will approach this as a bike that they have to sell for little or no profit. It made its value by selling other bikes. You know the dealer better than I, but I think you might get a better deal with ancillary items than a straight-out low price.