I'm just wondering if I happen to have Athreos, God of Passage and Lifeline in play a the same time if they are essentially working at cross purposes.
Like it seems like the Athreos, God of Passage would bounce the card back to my hand preventing the lifeline from functioning the way it's intended too, right?
Indeed, if Lifeline's ability triggers, but then the card it refers to leaves the graveyard (whether by Athreos's last ability or otherwise), Lifeline won't return that card to the battlefield "at the beginning of the next end step"; in general, this will be the case even if that card returns to the graveyard before it would do so (C.R. 400.7, 108.1). See also this thread and this thread.
Like it seems like the Athreos, God of Passage would bounce the card back to my hand preventing the lifeline from functioning the way it's intended too, right?