If you were able to fully be like how you were before your mission it would mean you forgot everything about that, most probably. And that's just no good, no matter what it's part of your life, a very big and important part. That kind of thing shouldn't be forgotten, no matter how bad they may have been.

[He doesn't mind forgetting the good times that much, he doesn't have that many to remember to begin with. But the bad times he wants to remember, if only so he doesn't forget why he's the way he is.]

I suppose it's a small relief, to know that even after thousands of years one can still go back to how they were, even if it's a little bit.

[Though at the moment he's not sure if it would be worth it in his case.]