It is true that on some starts you can die within 40-70 turns, especially if you’re just starting with the game and have little clue of what is going on.
There aren't many. I used to think the Turn 15 rush by 5 Warriors was unbeatable, but now I realize the error was in building a Slinger as my first military unit. If you start with a Warrior or two before shifting to a Slinger, even the immediate Warrior rush can be fought off on most maps.
Maybe if you're attacked by Teddy on his continent in the first 25 turns and you don't have at least one 2F/2P tile in your starting ring you could be in trouble. I haven't seen that scenario, but Teddy would be the deadliest possibly immediate neighbour and if it takes you a while to build up your defence force, maybe he could take you out despite your best efforts.
Basically, surviving the first 50 turns of a Deity game starts with deciding where to put your Capital. It's not the same decision as when playing Prince. The first and foremost consideration on Deity is "where can I put my Capital that will make it hard to lose if an AI army marches on it on Turn 15?" That's either based on good protective defensive terrain or good yielding tiles that allow for a quick military build up or some combination of the two.
Once you have your Capital in the right place, it's what do you build first? I prefer Builder, even if an AI city pops up a few tiles away on Turn 3 or 4, as the Builder can be used to chop in a Warrior if need be. Then unless the AI is already mobilizing on my border, I like a Settler, as a second city means even the loss of your Capital isn't game over. After that, it's 3 Warriors followed by 3 to 4 Slingers, followed by an assessment of "how am I going to survive a Knight rush if the AI sends one?"
After you have an army capable of defeating an AI Knight rush, victory is just a matter of time. Play aggressively, play peacefully. Hand the keyboard over to your cat.
Doesn't much matter. The AI takes so long to win itself there's almost no half-logical path forward that doesn't result in a victory screen after you hit End Turn often enough.