Citadel - Hanar Diplomat - Personal experience

If Kasumi dies in the suicide mission, then starting the "Hanar Diplomat" quest will mention that the information was received from her prior to her death, at which point you are given speech options to optionally talk about how wonderful she was.

Other than that, nobody else takes part in the mission in her stead, you just have to go it alone.

Grissom Academy - Emergency Evacuation - Wiki

It looks lke if jack didn't make it, she is replaced by Ensign Jason Prangley:

After the battle, the students will say that their CO was killed, leaving Ensign Jason Prangley in charge. If Jack survived the events of Mass Effect 2, she will appear instead and berate Shepard for his involvement with Cerberus in Mass Effect 2.

This seems to heave a few additional effects for the mission and decision on how to use the students after the mission is completed:

If Jack is not present, a student will ask if you ever forget the first time you kill someone, giving you extra Paragon or Renegade points.

At the end of the mission:

If it's Jack, everyone gets out. If it's Prangley, he's shot and killed just before he makes it.

This doesn't seem to prevent the choice of what to do with them, just might persuade you to rethink it:

Once inside the shuttle, Kahlee Sanders will request that Shepard rethink having the students play a military role, especially if Jack isn't around and their their instructor and their student leader are both dead.

Attican Traverse - Krogan Team - Personal experience and Wiki

As mentioned in 's answer, Grunt is replaced by Urdnot Dagg if he died in Mass Effect 2. Functionally the quest is the same either way, with no change to the end of the quest where:

Grunt/Dagg will sacrifice himself so that that you can make it to your shuttle no matter which choice you make.

However, if you have Grunt and completed his loyalty mission in mass Effect 2, then there is a slight difference:

[Grunt] will survive the heroic sacrifice and return as a war asset (25).