Thanks for the replies!
Ok I am not an expert and am very new to the hobby myself, but I will offer my experience with DHG. I bought some from my LFS as kind of a "not sure if it will grow or not experiment" After planting in a new tank (no Drystart) It looked just like yours with alot of dying patches, but still some green. Like you I posted and found that mine was probaly grown emersed like yours and had to regrow new submerged growth. As the weeks have gone by (10 or so) I have been very suprised to see it make a full recovery and spread like a weed. Now obviously you are trying to drystart but, is it possible that the place you got it from had it submerged so long that it now has to transition back to its emerged growth form?? Im not sure just a theroy. From what I have seen so far its alot hardier of a plant than the internet makes it seem, I have sucessfully introduced a clump into my 10g low tech and its spreading quite a bit in like 2 weeks. I would say to be patient and as long as some makes it till flood day I think with your set up it will rebound.
If it were only dependent on the HC, I would flood tomorrow. But I'm worried that if I flood, the DHG will just float up to the top and I will bang my head on a brick wall somewhere.