If they haven't leafed out by now, they're dead.

The drought may not have been the only factor that killed them, but is highly likely to have played a big part. Last year's drought was severe and big trees need a huge volume of water per day.

Re-reading, I see that you said there were a few clusters of leaves present. From what I have seen, if large trees are damaged to that point, they're doomed. You could see what they do, but it sounds like they're gone. At this point, I think it's doughtful that lots of extra care would save them.

You could call your local extension office and see if they have an arborist on staff. Sometimes they will come out, take a look, and give you free advice. If it were me, I wouldn't pay an arborist lots of money to tell me the trees were almost dead, but if you can get help for free....

We've lost 4 Alberta Spruce, a Japanese Maple and a Redbud tree last year/this year because of last years drought.

My Dad thought that he had lost three of their huge Maples but we just had to go in and trim out the dead limbs on two of them. They had fully leafed-out but the other one had small clusters of leaves through out the limbs. I told him to give it a few weeks and just be patient; we could always cut it down if it didn't come back! Anyway I was over there Sunday and it was fully covered. They had a high-dollar Japanese Peach that looked like toast too but we trimmed on it and it's back healthy again.

So I guess the moral to the story or my point is that you can cut one down because it's dead ANYTIME but what's it going to hurt by giving it a month and seeing if it can bounce back?

I had a job this week where my customer asked if while we were there if we were able to take out three dead Box Elders. One was 30", one was 24" and the small one was only 18" in diameter. I cut her a great deal and we blew through 'em in four hours, easy money! Ok, so they weren't totally dead but they are garbage Box Elders that bring in Box Elder bugs so they're down, cut up and burned now.

So if they are nice trees rather than junk trees then I try and give them every opportunity to survive.