Personally i either want Grandpa to die just because of the sliding years of Homer/Marge's marriage/birth of Bart keeps sliding, whilst Grandpa being a WW2 veteran to be too integral to his character to be altered, i would think that out of all the characters, Grandpa should just die. at least Krusty has his sleazy yet funny moments, and Sideshow Bob was always a lark before the Italian episode. but in all seriousness, Homer and Marge was last in their late teens during the NINETIES, even considering the sporadic disappearance of Mona Simpson, Homer being born looks unbelievable when he's supposed to be 30-40 years old. (no, it does not help that Grandpa once said he was a toddler in WW2)
What if Poochie dies? they'll probably pull a Family Guy again and say a character dies, but turns out to not be important, it hasn't been the first time that Poochie's existence has been mentioned before, it's been referenced more than Principal Skinner's real identity of Armin Tamzarian.
Or what if it IS Sideshow Bob, but gets into a 3-way fight with Sideshow Mel and Cecil? maybe they plummet off a cliff and pull the whole "Nedna" thing all over again, letting their death settle before doing any plots, could either go that Sideshow Bob hastily studies Mel's Mannerisms so that he can imitate them to get close to Krusty but falling to his death causes Amnesia making him a replacement like Fat Tony being replaced by Fit Tony...who turns fat again.
Eventually Bob gets into the Mel persona, he tolerates Krusty, until something snaps within him, maybe seeing Cecil looking like Bob acts up the audience-surrogate side of Mel, defending Krusty/Bart from Cecil? then it turns out that Mel never died, Cecil did. for extra [annoyed grunts] the death should be falling off Springfield Gorge, because people has has enougth of that memory, right?