Yes, although that is easily determined via the second parameter,
However that is not the issue, which is - I am still left with an empty sub-window.
EDIT: Seems that we have reached a dead end on this ie there does not appear to exist a function to remove orphaned sub-windows
However there appears to be a potential workaround using ChartApplyTemplate()
Some downsides are that EAs will have to be reloaded. So not an optimal solution
Probaly a better solution would have been to use CHART_WINDOW_IS_VISIBLE., unfortunately it is read only
Finally resolved the issue. It seems that I required an additional ChartIndicatorDelete() before a loop to delete a remaining indicator in the sub window. Ovo's comment tipped me off to the problem.