Root rots are the result of poor drainage and are not helped or relieved by a fungicide application. If that is indeed what's wrong with you lilacs, then you need to select something that doesn't require really good drainage. And that tends to be a rather short list, unfortunately.

Did you plant the lilacs and know the age and variety? Did it topple and pull out of the ground or break off near the base? Have you dug up the roots to see what the roots look like and if it broke, what do the stems look like at the break, alive or dead? Does water collect there or is the soil constantly really wet? Does it have a swampy smell in warm weather or just smell like regular dirt? I am just trying to get more info since if there in fact another cause, my suggestions may not work for you. If you have a photo, that might help as well.

Also, you want to know your growing zone since Maine ranges from zones 3-6, a 30 degree difference in the average lowest winter temperatures. You can look up your zone on the map linked below.

http://planthardiness.ars.usda.gov/phzmweb/interactivemap.aspx

For my area, moisture tolerant shrubs include:

Rhododendron viscosum/swamp Rhododendron with scented spring bloom,

Clethra/summersweet which has late summer flowers and gorgeous yellow fall color,

Itea virginiana/sweetspire with later summer flowers and red fall foliage,

one of the shorter cultivars of winterberry holly/Ilex verticillata (need a male for every 6 or so females to get the beautiful fall berries, their only spectacular aspect)

red-twigged dogwood, some of which have variegated leaves and some of which have yellow fall color but are mostly grown for winter red stems

one of the really small selections of the native white cedar AKA arborvitae, but be sure you get Thuja occidentalis rather than one of the less moisture tolerant species of Thuja. Most of these exceed you height requirements by a large amount and if you have deer that come that close to the house they will get eaten, but they are a wonderful evergreen if you can find a small enough cultivar.

The lilacs have toppled and it was easy to pull the trunks out of the ground because there was rot at the roots. In general, my soil drains pretty quickly and the lilacs probably spend more time being too dry than too wet. In fact, when looking at plants to plant along my porch, dry tolerance is more important than wet tolerance. The last few summers have been fairly dry and I underwater. The first lilac to go was one I never watered. My sprinkler system is set up to water the lawn. It doesn't reach the gardens. The previous owner was a divorced guy who ignored the gardens so I can't see him watering those lilacs. We've had the house for a few years. When we've had several weeks with no rain, I water the perennials around the lilacs. So, they've probably had more drought stress in the last 5 years than damp stress.

I'm in zone 5. I had a winterberry, but it couldn't take the snow shedding from the roof, so I dug it up and moved it. Every winter too many branches would break and the thing always looked was recovering from a bad accident.

Why don’t you check out Clethra/summersweet, variegated red twig dogwood, and panicled Hydrangea such as Quickfire and Limelight. None of them are overly fussy about soil moisture. Clethra has late summer flowers and gold fall foliage. Variegated red twig dogwood have green and white leaves and red winter stems, and panicled hydrangeas have summer flowers from some time in July until frost that start white and gradually turn pink.

Great choices Babs, I might also suggest Aronia melancarpa (chokeberry) or any of the native viburnums, not fragrant but great bird berries and fantastic fall color