how did rick and morty fake their deahts on the sun

They faked their deaths by jumping into a vat of fake sun , which the Knights of the Sun took as a symbolic sacrifice and accepted as proof they were dead.

What happened

Morty’s stunt on the sun spiraled into a solar-war mess, and when he and Rick needed to escape, they pulled off the fake-death bit instead of following through with the original bluff.

Why it worked

The knights interpreted the “suicide” as a noble sacrifice, so the peace held and the conflict ended.

Simple version

• Rick and Morty couldn’t sell the original fake-out.
• They jumped into a vat of fake sun.
• Everyone on the sun believed they had died for the cause.

TL;DR: they faked it by leaping into fake sun, and the Knights of the Sun bought it as a real sacrifice.