Arrow's never been on the brink for ratings. It's The CW's 2nd most popular show after Vampire Diaries and it beat out Supernatural and it was like that for it's entire season. I think you're thinking of Nikita. Sure Arrow looks like it isn't doing well compared to shows on other networks that night (it's on the same time as Survivor) but for CW it was ratings gold.
I'll assume you know, and that's good news, because I've been dreading the axe being dropped on yet another show I've committed to for awhile. It's just that every time I went to look up the show on the interwebs there was some mention of it having low ratings. As you say, it may have only been in relation to the main networks, and not to CW's standard.
I hope that Arrow is not in any danger, because once it got past the silliness of the first few episodes, like Olly learning to kill by having to kill... a chicken, or the plot-pivotal scene of his changing into full costume while running up stairs to intercept a sniper who was already shooting people, or all the relentless flip-fighting, it's become a pretty decent show.
In other words, Smallville Part 2
That remains to be seen. Just personal taste, I appreciate the moral ambiguity more in the world of Oliver Queen than that of Clark Kent.