Personally, I would hope that it'll be the latter. 

To once again use the Total War titles as an example (particularly MTW), if you want to kill/capture the enemy general (regardless of whether it's the human player or the AI making the attempt), odds are good you'll have to pay a high price in lives in order to do so.  That's not to say that killing/capturing an enemy general is impossible -- far from it -- but the army that does pull it off will often suffer an appallingly-high casualty rate.   

First you have to get through/past the main army's troops.  Tthen you have to cut down the general's bodyguards (which are usually among the best fighters the army has).  Finally, often times the general himself is a tough SOB as well. 

So if an army does try to take out your Channeler, then I would say yes, they should have a hard time doing so.  Even if your Channeler is only moderately powerful (relatively speaking), I think s/he should still last long enough that the enemy army will get mauled by your own troops in attempting to kill him/her.

This is something I had been wondering myself. The problem I see with making channelers powerful enough to take a beating is; what if you decide to "go Gandalf?" If an "average" channeler can survive an army for a moderate period of time, what about the channeler that has everything put into making him/herself stronger? Then "Gandalf" could just walk right across enemy borders. wade effortlessly through armies up to the enemy channeler's tower and duel them, and probably win, because "Gandalf" has focused on making himself stronger, while the other has been building an empire.

Trying to balance that would be very, very hard.

Ever played dominions? Maybe you should people.  But I never bring out my channel/god type unit till it's very well enchanted/protected, etc..except in begining of game maybe when he's untouchable.

While Scoutdog and kyogre12 have both raised very valid concerns -- ones which I share, truth be told -- I suspect Willythemailboy has hit upon one of the keys for keeping things balanced. 

If you do in fact "go Gandalf" and leave your nation behind, you risk losing it to your enemy(ies), and thus the source of your mana.  In addition, if your Channeler is off doing their best "conquistador" impression, then they're also *not* sitting in your capital researching spells, recruiting hereoes (and/or imbuing them with essence), etc.  So going Gandalf will likely have seriously detrimental consequences for your nation, in more ways than one.

I always assumed that a player "going Gandalf" would have no nation/empire/kingdom whatsoever. At least, that's what I got from it when that term was first coined (don't remember what thread that was, though) It would be a very, very different style of playing than usual. Of course, this is all moot if it turns out that going Gandalf, at least the way I envision it, turns out not to be a viable strategy, although I hope it will be, because different styles of play are always good.

Well the term "going gandalf" was coined by players, and the common usage of it, afaik, has deviated from its original intent. The original usage of it I think was just to describe a channeler who focuses largely on himself, his own power, without really having much of an empire or nation, or heroes or army. It has turned into the idea that you control a channeler, without any nation at all; at most maybe you'd have a small band of heroes and creatures. Personally I'd be really surprised if that's an option in the vanilla game...

My biggest reason for thinking this is that not long ago they told us that explorable dungeons probably wouldn't make it into version 1 of the game (now that the release date seems to have been postponed until August, that doesn't seem to be the case). However, if there were no explorable dungeons then going gandalf would be a pretty bland experience.

Other reasons why I don't think it'll be in the game is - how do you hold onto things like crystal shards (map objects) if you have no army to speak of? The mechanics of a channeler 'gone gandalf' would have to be totally different than the mechanics of a 'regular' channeler for this to really work out... Also, how would diplomacy work? And conflict? Being at war with a channeler 'gone gandalf' would be extraordinarily frustrating - you wouldn't be able to do anything to harm him other than to straight up kill him, or weaken him enough to force a retreat... And to do this you'd probably have to confront that channeler with the better part of your military force combined - a succession of smaller attacks would probably be wiped from existence in short order. So while you might hurt that channeler enough to make him temporarily retreat, you've probably lost a significant portion of your army, and maybe cities and infrastructure as well. That lone channeler, with nothing to lose but himself, will regenerate whatever hurt was done and be back soon enough; you with the empire would have the daunting task of rebuilding and re-training...

In my mind, it seems like in order to make 'going gandalf' functional, the channeler would have to be too powerful to effectively balance against people building up empires. It's the same reason why having 1 dragon is usually a better option than having 1000 knights, even if 1000 knights are equivalent to a dragon in combat. The reason is that as you fight, even if you win, you'll slowly lose knights; whereas no matter how much damage is done to your dragon, as long as it hasn't been killed it's still there in all its glory. The only exception to this is that you can split up the knights to fight multiple battles at once; that, however, doesn't matter in the case of a channeler gone gandalf. What need would he have of fighting multiple battles at once? He only has one front: himself. He has nothing to defend or protect.. Except maybe shards, but if he has to actually protect his shards then going gandalf would utterly fail...

I also think it would be really cool; I just don't see it happening, at least not by release... Personally, I'd rather they focus on making the 'normal' game as good as possible, and work on something like this as part of an expansion pack. The addition of a totally different way of playing the game could easily be the focus of an entire expansion pack.

Have you ever played dominions (given how consistently and constructively you post on this forum I have to assume that you have)?  I think that having characters suffer injuries, some temporary and some permanent would be an excellent way to balance this.  That way you would still have a powerful character, but throwing him into battle against a thousand knights should not be done lightly, because even if you win you could be so weakened by injuries or loss of mana that you would be incapable of acting in a significant matter for quite some time.  That makes your character kind of like that empire you want to bring down.  It takes time to build him up, and time for him to recover from close fought battles, even in victory.