I will beg to differ here. I just ran a large C&G II Napoleonic wargame at a recent convention. It was part of an 1807 campaign we are involved in.
Two Russian Divisions and three Russian cavalry brigades were moving through a town and two French corps with other supporting units attacked them. This battle thus was "large" in that at least three corps worth of force was present.
Terrain was set up by 10:00 a.m. Battle developed as of 10:30 a.m. Wargame came to a conclusion by 7:00 p.m. with Russians withdrawing and fighting a rearguard action. Four commanders were present (two for each side), but one had to leave for two hours and one French commander handled both corps for awhile.
I've run other large wargames using computer moderated and can state (evidence if the form of witnesses to corroborate) that they all came to a conclusion.
I noted in a previous thread of a couple of months ago the many organizational things that we do to achieve these results and don't care to type all of them over again. If the operator of the software knows the software well and has experience (major factor), you are organized and have organizational aids (such as a large dry-erase board on a tripod which is used to record units firing at each other so that the operator doesn't have to get up and can remain at the laptop, large copies of the main charts on a presentation board on a tripod so everyone can see it, etc.), and you have a checklist and have indexed the rules book, you can and will complete large wargames using C&G II.
I noted in the other threads how all miniatures involved are organized prior to the battle by the "referee" in storage boxes with drawers (numbered on the outside of the drawers to match the unit and officer ID numbers used in C&G II). When a unit is visible it can be located and placed quickly. I also noted using thin sheets of thin, clear plastistruct stands ("sabots" as Der Alte Fritz would say), cut for various types of units (and labeled with unit ID numbers) to make movement easier.
I made unique measuring sticks with alternating colored squares for quick "at a glance" measurements, but also used grid strips (cut from grid sheets made of flexible plastic in 1/4" squares) for infantry firing range that can be used and left near infantry stands so you don't have to grab the measuring sticks every time. Also, C&G II remembers that range if the units firing at each other do not move or change targets.
I could type up six more paragraphs of organizational things that we do, but my point is that there are no regular (i.e. non-computer) rules that I've used or observed at Conventions that can come to a faster conclusion the size of wargames that we do. I must note that we use battalions as the basic maneuver unit and C&G II tracks individual casualties, fatigue, ammunition, and more. That is, more tactical articulation and more detail accounted for than brigades-as-the-basic-maneuver-element wargames.
There are no dice to roll and there is no rules-lawyering. The computer handles all combat, fatigue, disorder, etc. Each person focuses on commanding his units (you cannot argue with a computer). An operator knowledgeable with the software and accompanying rules can quickly decide about any issues that arise (and if you are a member of the C&G II Yahoo Group you can learn from the many questions and suggestions and thus be fully prepared for any unusual situations).
I've run the Napoleonic and American Civil War versions of C&G II with large battles and we always come to a conclusion. Sometimes a commander will decide to withdraw instead of slugging it out for no reason (in campaigns it is often wiser to do so).
I am not related to nor have any financial interest in C&G II.
Running a large wargame battle requires experience, knowledge, and organization. For those who claim it cannot be done--I want you as my opponent across the battlefield. I would rather command against someone who thinks something cannot be accomplished than someone who thinks it can.
P.S. Our campaign involves eight commanders. We're using a campaign system that I developed as part of a graduate school project some years ago and which has been refined over the years. Some of our commanders are two or three hours away, but orders and reports are handled via email. We can even have a battle if they are not present by using digital technology from a remote location (they are not present to push some units, but they are commanding nonetheless). Eleven campaign days have taken place in 33 real days (and there were a couple of breaks, such as for Mother's Day).
My point is "yes it can be done." You have to want to do it, figure out how to best organize (and always look for ways to improve things/alleviate problems). My goal of having all terrain placed in one hour or less has also been realized (and I'm not talking about felt and lychen sprinking).
If you are not willing to learn the software well and organize then you will likely achieve successful conclusions.