You can create a list or group of your end-of-line ancestors using RootsMagic.
Reports > Lists > Individual List > No parents
People to include: select from a list
Highlight the starting person and check their box
then click on Mark group, select "Ancestors of highlighted person"
Direct ancestors - set the number of generations
Click OK, OK, generate report
You can also create a group of your end-of-line ancestors and filter your list on them.
Create a Group - New
Highlight starting person
Click Mark Group
Select all ancestors of a person - direct ancestors only
Click Unmark Group
Clear people by data fields
Select "Number of sets of parents", "greater than" and enter 0
Click OK, OK, OK
Enter name for the group