Well, his ghost is probably up to something.
Oh hello Omake Bug, you're looking very friendly today - YEOUCH!
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Meanwhile, In Heaven...
God steeples his fingers as Perry arrives at the Throne. The giant, multi-ringed angel lights up, showing God's face through the angellic light like a monitor would. Ah, mortals and their wacky inventions.
"Ah, Agent P. On time as usual," God speaks approvingly as an image of the Devil in front of a familiar beachfront appears next to His face on the Throne. "The vile Dr. Devil has been summoned by a small child in San Fransokyo. He has not been heard from in days, but this strangely worded letter of distress he sent to Me has Me concerned. Find out what he's up to and put a stop to it!"
Perry salutes and stands up, adjusting his iconic Fedora - Halo now included - and flapping his angel wings experimentally.
"Remember," God reminds the platypus more for the sake of tradition than any actual need for a reminder. "Your secret identity as an undercover Angel Operative is imperative to the mission, and you cannot let anyone know lest there be dire consequences. Good luck, and you have My blessings, Agent P."
A Choir of Angels begin to sing a classic song as Agent P runs over to a tube-like gap in the clouds and flies down to San Fransokyo.
"Doobie-Doobie-Doo-Wa! Doobie-Doobie-Do-Wa! An-gel A-gent
-P!!!!!"
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As Doofenshmirtz takes a bite of his Quality Bratwurst Sandwhich, he turns to look out the window, barely missing the winged Platypus Spirit fly by.
"Huh. An immense feeling of nostalgia, sorrow, and satisfaction at knowing that wherever Perry is, he's doing what he loves just came over me..." He says distantly, looking back into the room. "...I think I'll take a walk through the park later this afternoon. I must be having one of those moods TECHNOR, the Mechanical Man, warned me about."
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...I blame the Omake Bug.