Firstly, Rand's assumption that the fading of the webs of Compulsion signalled her death are erroneous. Weaves such as Compulsion are generally set and remain regardless of whether the channeler dies. Indeed, the Warder Bond still has an effect on the mind of a bondmember who loses the other - it doesn't simply vanish.

Secondly, Graendal is not an idiot. I say this because we already know what her modus operandi would be - she came out and said it much earlier in the series. 1) She would throw herself at his mercy counting on his treatment of women and 2) She would flee and go to another base of operations. This second answer, it seems to me, to account for her treatment of the noble Rand sent. It seems to me that once you get a messenger from the Dragon Reborn at your secret palace, it is time to escape as soon as possible, because he is at your doorstep and has destroyed other formidable opponents. I don't think she would know about Semirhage's death, but I also don't think it's important - Graendal isn't the type to risk a confrontation given how disastruosly Semirhage's went. Also, and most luckily for her, she did well to create chaos and cripple Arad Doman. Even better, she knows that Rand has done something even more terrible than her Compulsion - he's removed innocent souls from the Pattern never to be Reborn. This will cause him pain in the future, especially when she re-appears. Even worse, he duplicated a tactic that Aes Sedai and Forsaken in the Age of Legends had abandoned as being detrimental to the Pattern - who knows what he has unleashed in the space/time continuum of the area?

Finally, if she is alive, I think her next base of operations - Shara, which she already knows enough to Travel to since she has the Sh'boan/Sh'botay. Even more ominous is that it perfectly fits with her habit of adopting bases of operations that are far from the other Forsaken's.

I think it interesting that Rand doesn't consider the obvious - inverted wards to sense a male channeling are probably erected all over the palace and the surrounding grounds - she may have well had an alert as soon as he used the access key. Even more obvious would be a humongous light boiling in the air in a forest not quote out of sight of the palace. She may have very well used her Compulsion, sent the nobleman back in a hurry while gathering her angreal, useful servants and etc, and then seeing the bar of white light forming, Travelled away from the area immediately. Bel'al himself realized what Moiraine was weaving based on the reaction in the air before her, and she was handling a far weaker amount of saidar to generate it compared to what Rand held. Plus, the palace itself, not being a fortress, probably has many more vantage points to see from. Heck, Moriding could have woven a gateway, informed her that the Dragon was on her doorstep and that could have been why her Compulsion on the nobleman was so thick.

Also, I think she killed Asmodean - thought so for years and even if she is now dead, that doesn't remove her from the list of suspects.