I did Arrival after I completed the main story...however I'm wondering if it's going to be worth playing through the end again, otherwise my after-game save might not include progress from Arrival....

Well, just another excuse to do the Suicide Mission again and not lose anybody

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I think the import save you use for ME3 is different than what it was like from ME1 to ME2.

I think this time you are actually importing a manual save that has been made anytime after completion of the main story. So it should work fine.

When i looked at my newly added dlc achievements for ME2, the last one i got fom the main game was over 2 years ago.

I hope you can change the appearance of the character of the save carry over to ME3, my Shepard looks grizzled as strawberry float.