Pia, even if you trimmed the ROS it shouldn't have killed it..the worse would be lack of flowers.
Something's up cause I lost 2 trees this yr too..an 8 yr old Butterfly bush and 4 yr old Flowering Almond..they've been healthy specimens all these yrs..while working outside, I noticed there wasn't any growth on either plant..Sure enough, branches were totally dead..the FA had nothing but black stems/trunk the BB all brown..FA broke to crumbs in my hands..We dug out the BB yesterday..I don't understand..Give your ROS more time since sometimes they're late coming up like their cousins, Hibiscus..Toni

Rose of Sharon are Hibiscus (not cousins)...Hibiscus syriacus.

If you had a late freeze like the rest of us in the middle of the country, I would suspect that is the culprit.

Chances are it was beginning to come out of dormancy prior to the late hit.

I am still seeing the effects, since it also knocked out plants' immunities.

I prune my RoS's for shape every year and I've never lost blossoms. I usually shape it in the late fall or very early spring (long before it starts to leaf out).

If the wood is still green you might have a chance at saving it. If you've had trouble every year for the past 3 years it may need a different spot (more sun?) or it may just be a weak speciman.

best of luck