Did you find your Ira Lusk? What are his dates? His son Charles (b. 29 Nov 1835 and died in Murray, Orleans, NY) was born the same year that a Samuel Lusk (1780-1835) died. That would put him in the same generation as Samuel and Comfort (Hull) Lusk's children. Do you know if Ira was a brother to Samuel or possibly a son? There's the possibility that one of Samuel's sons named his son Ira (b. abt 1838) possibly after an uncle or brother? Have you found Ira or his parents since you posted this message?
As for disappearing from Orleans County, my Phebe Lusk (b.1815) moved with her husband, Nathaniel Huntoon and 6 children to Clinton County, MI. I also noticed on the website for Glidden Cemetery that Samuel Lusk's wife Comfort is buried in MI. Thinking that my Phebe is the daughter of Samuel and Comfort, I thought she followed her brothers and mother to MI. I found several of them in the 1870 MI census that the Library of MI has online. The family ended up in Branch county, MI in 1870. It looks like Comfort Lusk (b. abt 1794) was there with "sons" Cyrus (b. abt 1817), Silas (b.abt 1819), Elias (b.abt 1811) and Samuel (b. abt 1822) as well as "grandsons", Ira (b.abt 1838), Richard (b. abt 1838) and Alfred (b. abt 1843). So that's where the Samuel (or rather the Comfort) Lusk branch went to.