Попробуйте это.
СРОКИ БИТОВ:
func! IsMostBottomRight(nr)
let oldw = winnr()
silent! exe "normal! \<c-w>l"
silent! exe "normal! \<c-w>j"
let neww = winnr()
silent! exe oldw.'wincmd w'
return oldw == neww
endfunction
" echo IsMostBottomRight(winnr())
ИСПРАВЛЕНО:
func! IsMostBottomRight()
let oldw = winnr()
silent! exe "normal! \<c-w>l"
silent! exe "normal! \<c-w>j"
let neww = winnr()
silent! exe oldw.'wincmd w'
return oldw == neww
endfunction
" echo IsMostBottomRight()