Sif had no reason to miss Loki. They had never been close, and had been just short of outright hostile since he turned her hair black. She wouldn't actually get him killed while they fought together, and that was the extent of their relationship. Nothing would change with him gone.
Even if they had been close, Sif would not have missed him. Loki had betrayed everyone. Odin, the All-father. Thor, her best friend since childhood and his brother. The entire realm of Asgard. As it was, she was surely happy to see him go. He could bring nothing but pain.
Thor, of course, did not miss the trickster either. They had been brothers, and fought by each other's side more times than anyone had bothered to count, but Thor knew all of Loki's betrayal and lies. Trying to become king, trying to make Thor guilty enough that he would never think of coming home. Telling the blonde god that father was dead, all but by Thor's own hand. Inviting the frost giants. Every step, planned or taken advantage of. Thor wondered if he had tried to push father into the Odinsleep, a dangerous one, by all accounts, and one he fell into after being with only Loki. Either way, Loki had not hesitated to turn the event to his advantage.
So neither Sif nor Thor spared a moment in mourning for a lost friend, or brother, or anything else Loki might have meant to them. Neither sat on the edge of shattered Bifrost and stared down at the stars. Neither hoped the trickster was alive, nor that he might be brought back.
Heimdall saw, and left them to it. Everyone understood, though none of them spoke of it.
They all didn't miss Loki.