Although Mr. Nowlan left a preliminary mold of the work, it was not immediately clear if the sculpture could be completed by others.
Richard Hayden, statue project manager, was unavailable for comment. The Nowlan family said through Palmer that "it's too early to say what the status of that memorial will be and how it progresses."
Born in Philadelphia, Mr. Nowlan was raised in Overbrook and lived in Merion before moving to New England.
A 1983 graduate of Archbishop Carroll High School, he earned a bachelor's degree in fine arts from Millersville University in 1987 and a master's degree from the New York Academy of Art, Graduate School of Figurative Art, in 1996.
In 1995, he was invited to serve as artist-in-residence at the Saint-Gaudens National Historic Site in Cornish.
He held the residency, a prestigious position for a young sculptor, for five years and became immersed in the work of Augustus Saint-Gaudens, an Irish-born American sculptor of the late 19th century.
While at Saint-Gaudens he met Heather Wiley, who was serving as a Student Conservation Association intern. The two married in 2003.
Mr. Nowlan set up a studio in a former church in Windsor, Vt., across the Connecticut River, several miles from his home. The church's cathedral ceiling allowed him to work on a huge scale.
As his talent for sculpting figurative and bas-relief likenesses became known, he received important commissions for private and public installations.
In 2000, he created the National Wildland Firefighters Monument in Boise, Idaho, and the statue of Ralph Kramden, Jackie Gleason's Honeymooners character, for the Port Authority Bus Terminal in New York City.
Mr. Nowlan was commissioned to develop sculpted awards for music channel VH1 and the ESPN ESPYs. In 2002, he created a seven-foot-high angel fountain at the Cornish Colony Museum, and the Windsor Vermont War Memorial. The latter features a soldier modeled on Mr. Nowlan's own father, who was not alive to see it.
"He took his dad's real dog tag and pressed it into the palm of the statue," Palmer said.
In 2007, after years of work, Mr. Nowlan unveiled a tribute to 1939 Heisman Trophy winner Nile Clarke Kinnick Jr. for the University of Iowa. The school later commissioned him to do monuments to legendary swimmer Jack Sieg and Olympic wrestler Dan Gable.
He created a bronze sea-life for the Marine Biological Laboratory in Woods Hole, Mass., in 2008.
In 2012, Iowa State University unveiled Mr. Nowlan's life-size monument to track and field coach Bill Bergen. Early in 2013, Kimball Union Academy unveiled a powerful wildcat sculpture on its Meriden, N.H., campus.
In person, Mr. Nowlan was warm and friendly.
"When [he] sculpted a subject, he really got to know them, or their family, on a very personal level," Palmer said.
Surviving, besides his wife, are a daughter, Monet; a son, Teelin; two brothers; and four sisters.
A public memorial service will be at 4 p.m. Friday, Aug. 9, at Saint-Gaudens National Historic Site, Cornish, N.H. A local memorial will be scheduled.
Donations may be made to an educational fund for his children at People's United Bank, FBO Heather Nowlan, 50 N. Main St., Windsor, Vt. 05089.
Contact Bonnie L. Cook at 610-313-8102 or firstname.lastname@example.org.