Tarquin will be killed...

[thereaper]

...By his party members.

Maybe he planned for Nale to kill Malack, maybe not.

But I would not be surprised if Tarquin and his party appear in the desert, and Tarquin's allies turn on him, believing that he had orchestrated Malack's death.

"So let me get this straight. Your son, the one that tried to mess up the whole plan a while back, appears and gives you a way to potentially control the whole world, and you left him here alone with Malack, who he managed to kill on his own despite being incompetent and far weaker? And you had nothing to do with it? Yeah, I'm not buying it. Get him, boys."

It would be a very ignoble end for Tarquin that would neatly remove him from the story (not to mention possibly solving the problem of his allies too, assuming they need Tarquin to make the plan work) and simultaneously feed into the story arc's theme of mistrust. It could wrap up all the loose threads of this story arc (save Ian and Geoff) in one fell swoop.

And all without Elan needing to lift a finger.

[Bird]

And all without Elan needing to lift a finger.
I think that's my biggest issue with this idea. Elan just gets let off the hook? His conflict with his father is going to vanish without any narrative payoff?

Granted, we saw some character development in the illusion where Elan moved further towards an acceptance of familiar flaws, but we haven't seen that new attitude put into practice in the real world yet. I figure Elan will get the chance to flaunt his development with both Tarquin and Nale.

His secret plan with Durkon is still to come, also.

The other thing is, Tarquin is a smooth talker, and he presumably knows his party members very well. It would be odd if they saw a complicated situation involving Malack's death and jumped to the conclusion that Tarquin was to blame. Unless Tarquin had been framed extremely well, he could talk himself out of the situation.

[jogiff]

I don't think so. The Giant specifically had Elan come up with a way to defeat his father without making him look cool. He can't have Tarquin defeated by his other son without Elan getting the chance to carry out his plan.

[Jay R]

Am I the only one who thinks that Elan's secret plan for his father has already been revealed?

In the illusion room, we saw Elan's ultimate fantasy, and it was Durkon's friend Malack marrying Tarquin back to Elan's mother. This would make his father settle down and become a good man.

Note that Elan's plan isn't just about defeating him (http://www.giantitp.com/comics/oots0836.html).
Elan: I just had a totally awesome idea!
Roy:For defeating your father?
Elan: Yes! No! Sort of! Oh man, it's perfect! I just need Durkon to help me when he gets back.