So there exists an inconsistent workaround. So called '24h trick'. Basicly if you disconnect, dont log back in on the character for about 24h and after you wait there is a *chance* your save slot will revert to before entering the set (u dc on lets say 186, save slot resets to 181). DD community tested the timing of it for a bit and 24h seemed to be usually the break point.
Once you dc in dd, try doing a data center travel. You will get a message that your char is in an instance and cant travel. While it does not dissapear after waiting, it is a proof that sever holds the data of the disconnected instance.

My personal testing and observation suggest that it is tied to server load. Like its not some hidden timer that will expire your duty, but i believe the server will classify the instance's data as less important than players that are online, so when there is a need it will free that data and thus revert your save slot to previous state. What supports this is observations such as people recovering their save files after even few hours in early days of dawntrail suggest that its server load and my testing was during very low player congestion time and i could not get it to work even waiting up to 3 days.

Server maintainance also seems to reset your dc'ed instances, i personally had this happen on dawntrail release.