Was Subcommander T'Rul initially meant to be a permanent character on Star Trek: DS9?

Question

I remember when the Defiant initially got its cloak, the cloak came with a supervisor, Subcommander T'Rul. She featured prominently in the episode, and I expected to see her in later episodes — as she was the cloaking devices supervisor. You get the impression that DS9 is going to have a (semi) permanent Romulan character, even though (to quote Memory Alpha):

Upon being introduced by Benjamin Sisko to the senior staff of Deep Space 9 she bluntly told him that she "was not here to make friends".

This seems like a pretext for more character exposition, wherein she actually does become friends with everyone in an Odo sort of way.

She however never appeared after this episode. What came of this? Why do we never see her again?

Answer 1

I've got a partial answer. Subcommander T'Rul was depicted by Martha Hacket who later went on to depict Ensign Seska. According to her Memory Alpha article:

... she was called in to play Subcommander T'Rul, a Romulan on Deep Space Nine, in the episodes "The Search, Part I" and "The Search, Part II". It was then a director called her, saying they wanted her for a role coming up later that season, on the new Trek series Star Trek: Voyager.

So one could infer from that that her tenure on DS9 was indeed intended to be a temporary part as other plans for her quickly developed.

Answer 2

This was addressed in the Deep Space Nine Companion. In short, the answer to your question is a qualified yes. T'Rul was indeed intended to be a regularly recurring character, coming as part of a package deal with the cloak seen in DS9: The Search.

The producers then decided that they had had insufficient material to justify her presence (especially given that the cloak wasn't going to be used again) and Martha Hackett was released to work on Voyager as Seska.

A few episodes later they did decide to bring back the cloak, but since T'Rul's only real purpose by that point would have been to operate the cloak (and given the unavailability of the actress) the decision was taken to simply replace her with a couple of lines from O'Brien and Dax to show that they know how the cloak works without assistance.

With the mandate that the new vessel would have a cloaking device, Teleplay Writer Ronald D. Moore contributed one more component to the Defiant, at least for the season's opening two-parter: a Romulan crewmember. "We had a notion that we were going to keep the Romulan engineer on board as a permanent fixture to operate the cloaking device." Moore says. But the producers quickly realized that the new character would not offer enough story material to justify making her permanent. So T'Rul left DS9 after "The Search, Part II" (which left her alter ego, Actor Martha Hackett, free to sign on to Voyager as the villainous Seska).

Ironically, although the producers had fought hard for the right to install one on the new ship, "by the time we ended the two-parter, we had given up the cloaking device," laughs Moore. "We thought we wouldn't ever see it again. It wasn't until a few episodes later that we decided to say it was still there "

_{^{The Deep Space Nine Companion}}