i love that each side says "the other one gets *****-slapped"
but would they really fight with all of their forces? Yes, SBA speaks about them actually fighting, but i don't think they'd go all-out.
Rimuru's a guy who's not 100% the edgy fella (i know i'm speaking too much when i've only watched 1 season of the anime, but i'd bet money that he doesn't control his emotions to become one like, idk, Ainz/Momonga from Overlord.), To know that there's another guy just like him, miles away, who'd fight him immediately?
He'd suppose that it's a doppelganger or anything of the sort, not fight with 100% of his forces and capabilities to try and understand what is this thing just like him (Like, he won't let himself lose), and whey they understand that it's him but from another TL, they won't want to fight any longer.
"
State of mind: In character, but will attempt to win the battle. Characters will not give up of their own accord. That means a character that is uninterested or sees no chance of winning won't simply leave and characters wouldn't simply become friends with each other. This doesn't prevent a character being made to give up, because the other character manipulates them via things like, for example, mind control, fear inducement, psychological tricks or superhuman charisma.
Each character will view their opponents as enemies, who they have to assume wish to cause them severe harm such that losing could have any range of dire consequences. The characters will assume their opponents have not been forced into battle. They are assumed to have decided from free will to fight and are not excused by a just cause, difficult times or otherwise exonerating circumstances. Furthermore, the situation is assumed one where the opponents are not protected by social norms or consequences, such as being a civilian protected by law."
by my comprehension, doesn't feel like breaks any rules and they'd join forces to try and discover what made them encounter each other.
Also i'm pretty sure they'd revive the other somehow
effectivelly, incon FRA