In an interview with SF Signal, Glen Cook has confirmed that he is planning to write two more Black Company novels. The first, Port of Shadows, will take place between the first two novels of the original trilogy. He has already done some work on this book (in the form of two short stories which will be expanded into the novel) and will make this his next project once some other existing commitments are met.
There will be another book, A Pitiless Rain, which will be set after all the other books in the series. He does not disclose a timeline for this book. He also confirms there will be another Garrett, P.I. novel in the future, with the working title Wicked Bronze Ambition.
Cook also expands on what happened to his Dread Empire series, including the loss of the original manuscript (not just for the eighth novel but part of the ninth as well) and how he approached bringing the series to a final conclusion in A Path to Coldness of Heart.