I do though

Honestly, don't you two read! A Patronus doesn't kill them, it just sends them away. In Hogwarts: A History, it's written that Dementors are impossible to destroy- they are in a way immortal, though they were never alive, to begin with. Dementors die off eventually, the reasons and causes are currently unknown. A Patronus merely protects the caster from the dementors, by scaring them (dementors) away.

Yes. We read. But I know how to kill one. Use an infinity sided die

t h e r e i s s o m e t h i n g c a l l e d i m m o r t a l i t y

And there's something called breaking the 4th wall

I'll just pretend as if I didn't see that..