If your DP vanishes or goes missing on hitting rank 7 as a L30 character, taking L31 will restore it.
On reaching Rank 7 (legendary seems to start counting over from 1) without taking L31, my 4 extra DP obtained during L30 leveling all vanished. My ED tree showed 62/59. I tried to relog to fix it. It reset to 47/59. The 4 DP that should have been there was completely gone and it fully reset one tree and removed the last point I spent on another.
I wasn't deliberately banking XP -- was just exploring Isle and it wasn't worth heading back to take L31. So, when relog made things worse, I ported out of the quest, took L31, and DP was back to normal again. Other than worries that my character was perhaps permanently ruined, this issue didn't impact me much (noticed it at the start of solo'ing a quest, so no effort lost).
However, if you're deep in a quest and get a DC, you could potentially come back with one or more ED trees completely zeroed and no way to fix them short of leaving the quest to level up & respend.
If you take L31 ASAP, you shouldn't have any character issues. Putting the brakes on the zerg while you port out and run back out is separate thing. It could be a loong ride. Isle is HUUUGE and the teleports don't help much if you're new or haven't found them (they unlock like the ones in Giant Hold).