Sue him for the cost of replacement trees, and don't use him again.

Resin

So does this mean that the trees will die for sure?

This guy is also a neighbor (lives a few houses down)

Everything above the girdled area will die.
In all likelihood, they'll re-sprout from the root collar, and you can select the strongest of the several sprouts that will arise to become your 'new' tree - and within 2-4 years, one may not be able to tell that any harm ever befell the little trees - but you've lost whatever growth they've made up until this time.
Just another illustration of how a wide bed of mulch around a young tree can help protect against weedwhacker wilt and lawnmower blight - just by keeping them well away from the trunk.

If he has been doing your yard for two years and no trouble, perhaps he had his kid, or somebody else do the weedwhacker work this last time. A talk with your neighbor is in order.
Mike

What resin said.

Dan

Reminds me of the time I was called to a new-ish hospital campus in Hilton Head to inspect the trees that had been planted after the construction process was completed. The trees had been in the ground for less than three months and were ALL beginning to fail. As I recall, there were over thirty of them, maybe more.

When I made that site visit, I expected to find that the trees had been planted too deeply, which was usually the reason for this problem. Sad to say that each one had been girdled by weedeaters.

You can send us pictures of the damage if you want, but if the bark is gone so is the phloem. The trees will die. Don't let 'the yard guy' convince you that he can fix the problem with wraps or goop; it can't be done.

I hope you don't think that this can be ignored because he's your neighbor. He was hired to perform a service and is clearly not qualified to do so. I'd not hesitate to let him go, unless you've been EXTREMELY satisfied with his past performance. What if his judgement should lapse again or his lack of experience results in misuse of pesticides, fertilizers, improper pruning, etc.?

He shouldn't be surprised nor offended by you letting him go, and ought to be happy to replace your trees.

IMHO, your trees need to be replaced with LARGER trees. Reason I say that, trees of the same size would be growing roots, and not much in size over the next 2-3+ years. Your would have been growing larger the entire time. So I would expect replacements that once established will be basically the same size your trees would have been at that same point in time. Depending upon what kind of maples you have, that could be from 2.5" caliper, to 4" caliper.

Arktrees

Case law dicta is for either replacement of same caliper or monetary award based on approved valuation method.

There are an awful lot of clowns around here with mowers and string trimmers leaving dead trees in their wake. Likely similar in many areas.

Dan

One Japanese maple I deal with was knawed by voles ALL the way around, 2-3" band. I told customer it would die. He asked me to leave it 'just in case'.
2 years later... it's still alive. No sign of healing mind you, but clearly there is an amount of surface bark than can be removed without a tree being killed.