Cartman's point of view during Kenny dies. Spoilers for said episode.
Note: I do not own South Park or any of its characters. Spoilers for Kenny Dies. Cartman could also be considered out of character depending on whether you believe Cartman was genuinely upset when he heard Kenny was about to die.
The day he hears that Kenny is dying his only goal is to save his new best friend. He's never had a best friend before but he's pretty sure that best friends need to save each other's lives if the situation comes up. And when he hears that stem cell research, well, at least he knows what to do with all those fetuses!
The next day though, Cartman gets to thinking. Kenny always comes back! Why should this time be any different? And why should he waste the stem cells on saving Kenny if Kenny's going to come back on his own anyway? Better to save the stem cells for something Kenny and he can both enjoy, like another Shakey's Pizza! That's it. He'll keep it a secret and then Kenny and he can be the first ones to eat there!
But the day after Kenny dies, he doesn't come back. But the Shakey's isn't done yet so maybe the next day. Of course all Stan and Kyle about is that Kenny's not there right at that moment. God those guys are so selfish! Can't they think ahead to when Kenny's going to come back? Kenny's going to want Shakey's Pizza then and if Cartman had used the fetuses to save Kenny then they would only have one Shakey's Pizza and Kenny would probably die sooner or later anyway. But no, all they care about is their own selfish desires! Well, when Kenny comes back he'll help Cartman kick their asses because that's what best friends do; they stick together.
The day after that Kenny's still not back even though the second Shakey's complete and Cartman can't keep people out. Oh well, it's Kenny's own damn fault and he'll just have to settle for being the hundredth or so customer. He sneaks into Kenny's room (figuring that he'll hear him in there, wherever that douche bag is) and tells him that but the asshole doesn't even answer. Some best friend!
After two more days go by Cartman starts to get nervous. Kenny always comes back the very next day! What the hell is taking him so long? Another day and Cartman starts wondering if he made a mistake. Maybe he should have used the stem cells for Kenny after all. But no! Kenny must be hanging out in Heaven getting all the angels numbers. Cartman will have to yell at him if- no when! Kenny comes back. Bros before hos!
Then another day passes and yet another. Finally Kenny's been gone for two weeks and sneaking into Kenny's room again all Cartman can say is,"I'm sorry, Kenneh."