Command-K, Command-Up to do open a new vertical split pane in Sublime with the current file.
Command-K, Command-Down to close the pane and move the file back, or just Option-Command-1 to switch everything back to a single column no matter how many were open.
I've used split management in Sublime. I can say with some certainty it is awkward to work with compared with VIm's. Perhaps that's partly because I'm used it it.
One pet peeve I have is that Sublime came with a VIm mode package but yet didn't implement the split behaviours for it. Also you can't "open in split" which is supported in multiple ways in VIm.
Command-K, Command-Up to do open a new vertical split pane in Sublime with the current file.
Command-K, Command-Down to close the pane and move the file back, or just Option-Command-1 to switch everything back to a single column no matter how many were open.