Solution 2 (e.g. MoM) : player is moved to a "limbo" where they cannot cast spells or are otherwise severely limited, and must cast a "spell of return" to return to the normal state
- con: copyright infringement
- con: in MoM, it was rare for a wizard to actually succeed in casting this, so it was sort of just prolonging the inevitable, but it made it harder to win with 1 city versus 40 cities just by ganking a wizard (if they had enough, they could come back pretty fast)
- con: may be tedious to take out the remains of the player's empire and thus win the game even when the victim has no reasonable chance of success
I disagree with all the cons
In Dominions, you have the same system, except coming back takes time, so it's a startegic choice whether or not to call back your pretender god. So:
-pro; Additional strategic choice.
And it's VERY common in Dom for a pretender to die and be called back.
Overall, although one must check how it works out, having one unit that, if you kill it, eliminates the oppoennt sounds very bad. Why would you make your own unit weaker knowing that if it dies, you've lost? It sounds like the only reasonable strategic choice with such a system is to make your channeler as strong as possible and use it to trump weaker channelers (all by himself if you can rush tha fast).
Furthermore, if you can control units in tactical battles, it will be worthwhile sending for instance all yoru archers against shielded infantry, having the archers all shoot at the opponent channeler, get slaughtered by the infantry but kill th channeler. Result of the battle: You lose 20 units out of 20. Opponent loses 1 out of 10. You have won the game. At least make sure that a channeler cannot be targeted easily (no "Fire commander" orders as in Dominions I).
Overall, having game over if avatar dies sounds very bad to me as it looks like you can lose due to a lucky unit killing one of your units, and you will likely end up with a single viable strategy, of big tough channelers.