I have serious doubts the event chain will make characters immortal. More likely it will be just something to keep us entertained and give us a trait or two in exchange for gold.
I disagree, because the code for immortality, by default, has been in CKII for a long time. Paradox is just finally finding a way to include it in the game, so unless they change something to make it different, the default immortality experience will indeed make someone literally immortal to all things except assassination and death by combat. They can still acquire diseases and life-threatening conditions (ex. infirm and incapable), but they won't die from them.
The mod Dark World has been experiencing with this conundrum lately. In particular, anyone with the succubus trait could opt into immortality, including the AI, which the AI always did (I can't blame them)! However, it lead to very stagnant gameplay. The way around this was having a check in place where the AI would voluntarily commit suicide when they realized being immortality wasn't all it's cracked up to be, as their loved ones around them died off!
It will be interesting if Paradox includes something similar, or if they take the lazy route and release the immortality trait with its default settings. When Paradox speaks of immortality, I doubt they're lying. The code has already been with us for a while, so they'd be silly to refuse using it.