For being a immortal the Sovereign sure does die a lot 
Ok, to harken back to the days of MoM. (Yes I'm totally about to rip off a MoM idea). I don't think the Sovereign should die as long as he still has towns on the map. Perhaps limit that to only if the Sovereign has a "Rejuvenation Chamber" in that city. You can change that to anything you want as a building requirement *coughMageTowercough*. 
For an excuse as to why that should be possible? Well, you expel essence, mana, energy to bring the ground back to life so you can build there. It would only make sense that if your body is destroyed you could pull yourself back together at one of these spots. These places, I.E. cities are imbued with the Sovereign's very life energy, they are part of him. If they aren't destroyed, then neither should the Sovereign be. Just a thought. It would definitely enhance the game-play. It would also make every city of strategic importance in some way, even if it's just as a resurrection place. Maybe you'd need to build a Temple first, then have a level 3 Mages Tower, and then if you die while out adventuring your body reforms there after a bit of time. In order to truly Die the Sovereign's cities would all have to be wiped out.