I tried a number of solutions on here and none with any success. Since the only save file I had was from during the mission, I had no way to back out without starting from scratch. What I finally had to settle for was using the modified Gibbed editor (http://social.bioware.com/project/4373/) on the Save File to grant me the rewards (primarily Kasumi's loyalty) and try to clear the mission off the books.
I used an auto-save just before the final fight with Donovan Hock (at the point where the shields are down):
Get Shepard Off the Planet:
Under Raw > 1. General > Base Level Name
I changed the value to BioP_Nor which sets us back to the Normandy map
Also, under Raw > 2. Squad > Player Position
I changed each of the X, Y, and Z variables to 0
This had the effect of putting Shepard back on the Normandy safely
Get Kasumi's Loyalty:
Under Plot > Henchmen
Select Kasumi is loyal
Mark the Mission as Complete in Journal:
Under Raw > 3. Plot > ME2 Plot Table > Quest Progress > open Collection with ...
Upon getting the PlotQuest Collection Editor, there will be a list of Members on the right which correspond to entries in your Journal, complete or incomplete. I had to try to figure out which of the quests listed there was the one for Kasumi: Stealing Memory. Using the autosave at that point in the quest, I was at the sixth "part" of the quest (each line in the Journal within the mission apparently counts as a part). With PlotQuest Collection Editor window open, select one of the Members and then click on the History line in the right side, then on the ... button to expand the collection. This will open the Int32 Collection Editor and show a list of Members, with apparently one corresponding to each "part" of a mission. In this scenario, I had to find one that had six entries. This does not mean an entry with the number six as with most, they start counting from 0. In my case, this mission was number 26 (yours will probably be different). For some missions, each entry here had a value that matched the entry number (0:0, 1:1, 2:2, etc) but that was not universally the case. For this mission, the entries DID follow that pattern and I suspect that it will be the same. So upon identifying the correct mission, I added a new entry at the bottom and assigned it a value of 6.
Note that this did NOT eliminate the mission from the Galaxy Map. I haven't found a solution for that yet, but I may try. If you try to go back to the planet, I'm not exactly sure what will happen.
Once all is done, I saved it as a new save file using the format of the other numbered filenames (but prior to the highest-numbered one) and opened it up in game.
Obviously, the ideal solution is for there to be a fix for this but this much got me back up and running and I figured it might help someone else out if they were in the same position.
