Would the sentence 「田中さんはまだ来ていません」translate to “Mr. Tanaka still is’nt coming” or “Mr. Tanaka hasn’t come yet” or are both translations possible?
It means "Mr. Tanaka hasn't come yet." 来ていません means "being in the state of not having come." If you mean to say that Mr. Tanaka will not come (or in English, "won't be coming"), that's 来ません.
In general, Japanese uses progressive (ている) form in the negative to express the state for which English uses present perfect:
I haven't seen that movie yet.