Love the use of cadence to describe how berdley acts.

In my opinion berdley will have a roll to play in future chapters even if it is just a small one. We've seen some major character growth in chapter 2. completely writing him out of the story (weird route aside) would be such a waste of a character.

In terms of potential evidence. In the doctors office there's a small wire-bead toy thing. In chapter 1 it says "The beads march grimly along their path". With a similar message after a normal run of chapter 2. but in the weird route after killing berdley "(One of the blue beads is broken and torn off.)"

I think the game is trying to tell us that during the normal route the characters are fated to walk a certain path. And unless you do the weird route berdley is still fated to walk the path set out before him. He still has a role to play in the narrative. I think it'll be a more minor role I don't foresee another chapter devoted to him but there's still a path for him to walk in the normal route.

After killing him his death (or disappearance body could have been hidden or dusted after we left) will definitely still be a plot point because someone died/vanished that's a pretty big deal. Undyne will probably be on the case.

That's my thoughts anyway. I like berdley so I'm probably a little biased.