I think they both stabbed him but Wanderer basically gutted him.
The Details are less of my issue and more that we have -another- Multi Planar threat that was just let go that we won't ever deal with for 5 years until we get Duskmourn : All Will be One. Like even in the Bloomburrow story (which was filler) Gleb got away, it's a recurring issue in Magic's plot where the Villains just get away when its not particularly needed.
Hell Technically not even Bolas and the Phyrexians are permanently dealt with, if either figure out a way to get out of their current places they could come back to power. Especially now that they are introducing a..Transferable Planeswalkers Spark as an equipment....Bolas will want to get his hands on that shit.
Edit : The first episode of AetherDrift came down today, This is gonna be BAAAAAAAAAAD