5. Stewie's Time Machine
Fans clinging to even the remotest of hope that Brian can still be saved and brought back from the dead point out that Stewie has a time machine. Various Family Guy episodes depict said time machine, which has been shown to send Brian and Stewie into the future or back to the past, such as to Nazi-occupied Poland, among other places. It isn't inconceivable then for Stewie to just hop in his time machine and travel to a point in time when Brian was still alive to warn him about his upcoming demise, perhaps by saying, "hey Brian, don't buy that street hockey set!" Previous episodes have shown Stewie preventing people's deaths via his time machine, like Kurt Cobain ('Viewer Mail No. 2') so it isn't implausible the same can't be done for Brian. Ah, but there's a snag, because said time machine is shown in the same episode Brian dies to be irreparably broken, and that the parts Stewie needs to fix it are "unavailable". The argument that Brian cannot be brought back to life via the time machine stands up to credulity for all of five minutes, though. This is Stewie we're talking about, after all, a determined character who has been shown to do whatever it takes to kill Lois. And are we really expected to believe he would give up so easily in trying to save Brian, after just half an episode?