Well, they were pretty dramatic deaths and made for good tv but, well, you can't have your cake and eat it too, right?

Exactly, at the time it seemed like they surely must have been planning to bring the show to a dramatic close, it seems a bizarre choice otherwise to not consider how it would impact on the show to kill Ianto off as well, after they'd already lost Tosh and Owen. TW's appeal was never Jack and Gwen alone