Naw dude, that would’ve never worked for real. Ben’s Omnitrix has a bunch of failsafes to prevent it from being removed or to prevent Ben from dying, which would certainly include his arm being cut off. The second it was about to happen, The Omnitrix’s “Say No to Death” Failsafe would’ve kicked in and turned Ben into Diamondhead or Atomix or something, and those stupid-ass scissors would’ve done JACK SHIT. That Death Battle vid was completely loaded.
To be fair though, GreenLantern IS an incredibly versatile powerhouse, and against 80% of Ben’s aliens, he’d most likely win without issue, but Ben only needs one or two aliens that can beat him, and ALIEN-X absolutely qualifies.
It would be super cool if the Ink Tank did THEIR OWN Death Battle, and pitted Hal up against 5YL continuity Ben10!