I understand the DT system to work with trust and reputation of a user in the forum that makes other DT members to include them in their trust list and even though some users earn trust due to the assessment of their past behaviors to their present but i think that an inactive DT member should be removed because if a member can stay out of the forum for over 5 years, what will be the probability that they will come back to the forum someday and still maintain same level of reputation that got them trust from some DT members? Perhaps, for those who made it clear they won't return to the forum again, what is the essence of still leaving them in the DT? besides, the positive trust feedback from other DT members should be enough.
I don't know why this idea came to your mind, if removed them from DT does there will be any significant change to the forum other than lost the left feedback from them by default? Once upon a time they were active and contributed to the forum, and they gained enough trust; hence, they got into DT. So their feedback has a value; inactive doesn't prove their feedback wrong anyway. I am talking about DT2 since DT1 was selected by the new system, and inactive members won't be longer in DT1.
Positive feedback to the inactive DT members is not worth it when a person is inactive. Because he isn't going to trade with someone unless he becomes active once again. Trust me, I don't get the point of your post; it really doesn't make sense at all.