The townland of Coolcappagh is actually in the civil parish of Clonagh which is just to the east of Kilcolman civil parish.
I looked at the 1850 Griffiths Valuation head of Household listing for Co. Limerick and there were only eight Fallahy (or variant spelling) households. Only two were in the general area of Coolcappagh. They were in the civil parish of Rathronan which is between Kilcolman and Clonagh parishes.
I also looked at all civil registration events (birth, marriage and death) from 1864-1900 in the area around Coolcapple and there was only one event ( a birth in 1880) in the 36 year period.
So from what I can see the surname was very scarce after your family left.
Let me know if you have any questions.