This is correct. I can think of many reasons, ranging from everything from physical or mental health to various life events or circumstances, which would make an account suddenly become permanently inactive. As you say, if you or I disappeared from the forum tomorrow, it is highly unlikely that any other user would ever know why.

There are three potential solutions which I can see:
1 - All feedbacks are left as is, and the user has to be excluded from DT or have their ratings countered if not appropriate
2 - The community discuss and petition the admin to remove the inappropriate rating, while leaving all the other accurate ratings, as we are doing here
3 - There is a recent active requirement for you to be added to DT2 - much like you must have been active in the previous 3 days to become DT1, perhaps you have to have been active in the last 6 months to appear on DT2. This would not prevent users from adding the user in question to their own personal trust list, just that their ratings would not show up in DT.