Hello, JK JK. I am making some assumptions that may not be correct. Needed more info about the so-called late frost and things like watering. But here's a guess:

If watering the soil does not quickly perk up the leaves then the late frost zapped the leaves. But killed the plant? Weeeeellllll, these are tough plants and death by a late frost is almost unheard of (but not impossible). Late frosts would hardly damage roots but they would affect the growth above the soil line. Leaves would turn papery-like green and dry. Or they may turn dark green, almost blackish. To find out the condition of the stems or the main trunk, you can lightly scratch the cambium (sp.?) layer with your nails to see if you see green. And if the green stays green.

Covering the tree will provide s-o-m-e protection from frost buuut not enough if things get "frosty" enough. If the leaves got zapped by the frost, you should get new leaves later on (wait as this is not an overnight/quick process though).

But has something ELSE has occurred? If the late frost happened recently, you should get new foliage after several weeks of waiting. I would be concerned about the main trunk after waiting for leaf out and getting none in 2-4 weeks.

If something has happened that killed the main trunk, it sure did not affect the suckers. They look just fine so I have the same hope for the main trunk. But you could kill a main trunk other ways... if temps fluctuated a lot, stayed high enough to break dormancy and then the temps crashed well below freezing; new growth would start from the bottom as new suckers. Or something else happened like borer insects damaged the main trunk. Etc, etc.

The suckers appear to be several years old and are looking fine. So hopefully, if this pic is recent, it looks like the frost got to the upper parts of the shrub and not to the suckers. Something frost sometimes does.

In the meantime, keep the soil as evenly moist as you can, keep the soil well
mulched to conserve soil moisture and keep the soil amended/fertilized as usual (not
need to go overboard with more ferts or with more amendments; the regular amts should be fine).

Paniculatas develop new stems (suckers) from the base at times. Like yours is doing. Assuming that all is well with the main trunk, these suckers can eventually be pruned off like you would if this was a peach tree producing suckers. In the unlikely event that something did happen to the main trunk, the suckers can be used to re-grow the tree from selected suckers. But that is another story and I think you should first get confirmation that all is well (or not) with the main trunk.

Luis

Yeah, something caused the plant to abandon the main trunk and regrow from the crown. I suspect there was some sort of damage to the base of it. You more or less have a shrub now. You can train it back into a tree but it'll take quite some time (years). LL is a great shrub or tree (like #1 in my book), so if you can make use of it in any way, by all means try.

If that were me I would slide the shrub back a foot or two towards the corner to set it away from the roses. Within a couple years it'll take up the whole corner and grow all the way past the top of the fence!

You'll probably want to lop off that trunk anyhow.