Does the monarch death code take into account ages, so older monarchs are more likely to die? I figured it would do something with MTTH and each decade of rule, but I haven't found the code explained anywhere.
The other advantage of republics is you are guaranteed able to replace a crummy leader in the next election. Sometimes, you get stuck with a regency for a decade and then a crappy monarch for another decade until he dies in battle (and I make sure the bad kings lead from the very front of tiny forlorn-hope detachments).
Yes, IIRC you can even change it. (about the death possibility and age)
About republics, for some reason i have problems killing my president in a battle (noble republic terms last 8 years), compared to when i play monarchies, where most of my rulers are very good or at least average, and i don't have many problems with bad rulers.
If you get a bad president, you can reroll in 4 years; with a Monarchy you can be stuck with it for decades. Or he can die immediately and you get a 15 year regency council.
A regency can be better than the monarch tough, only downside is that it limits your diplomatic actions, but in ruling the nation? It isn't that big of a obstacle unless your heir is very, very awesome and/or the regency sucks
And you can just elect them till they die of old age, I've had great presidents like 8/9/8 for some 80 years and his successor being a 7/7/8.
Yes, kings also last until they die of old age tough, and they usually last more than presidents (from my experience anyway)
If you focus more on the rest of the world and not within your religious group, there's no reason to go Monarchy, the only significant advantage I can think of are PUs and inheritances (and what a crazy advantage), but if you neglect this for whatever reason, Republics are consistently better.
What? You can get as many good rulers as a republic, have legitimacy bonuses, royal marriages...not to mention that governments like empire get an universal CB (Empire Holy war -> Ab. Monarchy Imperialism...)
But if you ask me, the absolute best government at managing your nation is Const. Monarchy, it gets very good bonuses and a modifier unique to it (Division of Powers IIRC)
combined with legitimacy bonuses...trust me, it's a great government, better than any other when you take everything into consideration. Its only drawback compared to others like Absolute Monarchy is the sliders limitation and no imperialism CB (unless i'm badly mistaken here, quite some time since i last played Const. Monarchy because i usually just remain Absolute)
EDIT : Of course, that's not considering revolutionary governments...