Well, first things first: it's a Dracaena fragrans. I think. The reason why it hasn't attempted to grow back any of the lost leaves is because it can't. All you can do when you're a Dracaena is get taller or branch, and branching would only be likely if it had grown mostly horizontally for a period of time, or if it had flowered. So it gets taller. Is there a way to regrow? Well, kinda. You could cut the plant back, at which point it would be forced to sprout new growing tips. Or you could air-layer (.pdf file) and start over again with the tops of the plants. The more interesting question to me is why you're losing so many leaves in the first place. Granted, keeping your plant alive for two years is an accomplishment in and of itself, but the leaf drop looks like a fairly extreme case of something or another, too. It would like more light, though that's not why it would be dropping leaves. Soil breakdown is a possibility, as is over- or under-watering, fertilizer buildup, and temperature. Pests are an outside possibility, but these aren't really known for having pest problems, and most pest problems would have progressed well beyond obvious by now. So. When you water, do you pour water in until it starts running back out, or do you only add a little bit at a time? Does the plant ever have to stand in a saucer full of water? Is the plant in a draft? Is the plant in the path of an air conditioning or heating vent? How long has it been since the plant got new soil? Is the water in your area naturally high in fluoride? How do you decide when it's time to water? (by schedule? by feeling the top couple inches of soil? by weight of the pot? whenever you remember?) Are there roots coming out of the bottom of the pot? I'm going to go ahead and bet $10 on soil compaction and/or rootbound: that's a lot of plant for the size of the pot it's in. Unlike saucer, I think I would go up a pot size unless you're planning to cut it back, and if it's as potbound as I suspect it is, I might move it up to the next largest size regardless. If it were my plant. Which it is not. Look at the roots first, like saucer said.

I live in the Phoenix area and am having the same problem. Last year I lost two, well-established hibiscus (red) about this same time of the year. Those two got morning sun. It's happening all over again (also red ones) in a totally different area of the yard that gets afternoon sun. As far as watering habits, I run a drip line to the plants and water three times a day for about 7 minutes at a time. I currently have a row of six fully grown hibiscus. The one on the end has started to die first, and the one next to it is showing the same symptoms. Would this indicate the spread of a disease, as the bushes are all right next to each other? A photo link is attached. Help! Here is a link that might be useful:

this is why we prefer to plant trees in dormancy .. so there are no leaves to fall off ... severe transplant shock ... refer to teh link.. and discuss how you planted yours .. including how small a pot this large tree was in.. based on your small diameter hole ... https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub if you perfect watering.. so the roots start working.. there is a good chance it will releaf .. you ask if you should replace it .. well.. with what...??? .. if it wasnt a good time to plant.. then how are you going to plant a replacement ... did you get this from a good nursery ..... or BBStore??? ... i might wait and see if i could save it.. until they get their fall shipments.. and replace it them ... if you got it from a nursery.. ask them their suggestion ... never forget. .. just becasue you buy it.. doesnt mean it the best time to plant ... it took me killing a lot of things.. to learn to HOLD THEM OVER... until the next proper planting season ... i might have just put the pot in bright shade .. and waited until fall ... of course.. people in places that get 400 inches of rain and one sunny day a year .. and call 72 a heatwave.. do things all year.. that we cant get away with .... ken

mylifeeclectic very valid point, Even if elms are in a mild climate they usually react to the Winter and try to force themselves into at least a partial dormancy. It's for the best, if the tree didn't go dormant it would get exhausted... as it is not meant for continual year round growth like say evergreen varieties. I would stay away from any liquid based fertilizer. However if you have a soft slow release fertilizer for bonsai add some of the little pellets to the top. I would start to address the big leaves ASAP. Elms tend to grow long shoots of leaves. Proper foliage and branch structure is maintained by cutting these shoots down to 2-3 sets of leaves. this will allow for a more full canopy and stimulate growth. It also might be time for a re potting right now in early spring. I have care guides and tutorials on how to re pot Japanese Elms (which are very similar in care to Chinese Elm) Japanese Elm Care Guide Repotting Zelkova Bonsai