Brush some dirt away from the roots and look for little bumps on the roots, these will be the new branches. You can also scrape with your fingernail one of the roots to test for living tissue. If you scrape and its soft and green it's alive. Remember it grows brand new branches each year so the dead branches won't be coming back and can be removed. None of mine are growing yet, they are always the last to start growing.

Hello, If you bought a tree, it should not be cut down to the ground ever. I hope you bought the double bloom Roseof Sharon: Hibiscus syriacus the singles are notorious for hundreds of seedlings from 1 good sized tree every year. I have a few now, but there cornered and I plan to put a weed mat down. You should start seeing tiny green buds along your branches in the next 2 weeks or so. Although if they get hit with this freeze we have in the Michigan area tonight you'll have to wait awhile longer for new buds to form.

The hardy hibiscus 'bushes' we grow do indeed die back to the ground in fall and are removed all but a stub to mark their place in spring and you will not see hide nor hair of them until May, even late May - early June, most all will think them dead with their first experience with them but be patient it will come. And when it starts to grow it will be a bush in no time.
Happy Gardening - Sandy

The trunk is green. That means its alive. Hibiscus, at least around us, are just about the last thing to show life every year. My perenial hibiscus hardly ever look like anything until August. I used to have a beautiful rose of sharon at our previous house and every year, I was sure it was dead, even though I knew it just took a long time to get going. And every year it bloomed just as beautifully as ever.