It should be fine. What I want to know is does he need glasses?

You don't need to replace it - new branches will grow fom the roots. You do need to give it a defined edging in the grass so that can't happen again. Looks like the wire cage was removed to trim the grass within the cage. You might dig a circle in the existing grass a few inches outside the stakes, using a shovel or trowel, and remove the grass inside the circle. Be careful at the edge where the original pot outline still is to not damage the hydrangea's roots. Easiest to start at the outside of the new circle and work around the plant. (You can use the grass removed to patch the lawn in other places.) Then put down a rigid edging - four of those curved concrete edgers, heavy-duty plastic or metal recessed edging, a tree ring - set down in a slit or trench below the grass roots along that circle. Mulching inside the circle up to a couple inches from the hydrangea stems will help keep grass from the root area & benefit the hydrangea. Put your cage back around it. You may (or may not) allow him to weedwack carefully along the outside of that edging. Better yet, clip around it yourself with grass sheers before he gets to it.

Suspect we've all experienced these moments in one way or another. Recall one time my DH proudly whacked past the garden edging into a bed to take care of a "weed" - which happened to be a cherished plant lovingly raised from seed just about to finally bloom. One Autumn when I was ill, without saying anything beforehand, he "cleaned up" the porch flower beds of mixed perentials & roses, thinking to please me with this surprise "help". He left the Fall weeds, which often look so healthy, and pulled the perennials that were fading. Went so far as to shovel out a 20-year-old poet's jasmine grown from a slip & lovingly tended all those years, mistaking it for wild honeysuckle. Surveying the destruction, I did break down & sob, hard & long. The jasmine eventually managed to spring back from roving roots & revive. The rest was begin-again the next season, with a few rugged survivors happily reappearing. Our long marriage survived as well...

I actually go so far as to hide the weedwacker between uses. Best you can, prevent the possibility of your current heartache recurring. My heartfelt sympathy goes out to you!

If he wacked the plant with the chicken wire using the mower, I do not expect the mower to leaf out this year.

:o) Hee hee hee!

I agree with creating more space between treasured plants and the lawn. Create a wide area of mulch around a single plant or make an island of many plants so that trimming an edge (or weed-whacking) will not cut down young plants or remove the bark off trees and shrubs (slow death).

Do not pile too much mulch around the trunks as this may lead to rot and insect problems.

With this method you can eliminate the cage altogether unless you have rabbit - deer problems.