I don't agree with forcing people to complete rounds, unless you want to allow them to switch to the free balls mid-round. Even then, there's an easier and better solution...
All you'd have to do is calculate people's "average" on a per-hole basis, should they exit out of a ranked round, and there would be no incentive to leave.
The calculation would go as such:
score_on_holes_completed * par for the entire round / par_for_holes_completed
If you'd completed five holes, and par for them was 21, and you shot 22, and par for that 9 was 36, then the equation would produce the following:
23 * 36 / 21 = 39.43 for 9 = 78.85 for 18
Now, of course, someone might say that a player could quit out of the game right after taking a bad shot, having not completed the hole, which would make the equation register only the decent round that he was having prior to the current hole, which he was doing terrible on and did not complete.
In order to adjust for that, it would be simple, score the hole reasonably based on their progress (and add it into the above equation):
If they have already taken (par -1) or more shots (e.g. taken three or more shots on a
par 4), then add 1 if they're on the green and within 6 ft of the hole, add 2 if they're on or off the green and within 50 ft of the hole, and add 3 if they are more than 50 ft away from the hole.
If they are not at that point yet, however...
If they've taken their GIR shot and failed to make the green, count the hole as a bogey. If they've taken their GIR shot and made the green, ignore the hole.
Did they quit out after 2nd, non-approach shot on a par 5? Again, if it's in the
fairway and within 150 yards, ignore the hole. If it is over 150 yards
or in anything other than the fairway, mark it as a bogey.
Did they quit out on the drive? Did it hit the fairway? Ignore the
hole. If they're in anything other than the fairway, count the hole as a
bogey.
Of course, don't hold your breath waiting for WGT to implement anything like this. I just don't see it coming.