Yes, if works are needed to obtain salvation, they are needed to KEEP salvation. The Scriptures explicity say, as you point out, that FAITH alone in Christ alone is what saves us. A totally paralyzed person can be saved—without moving a muscle to do a “work” towards that end. James points out that such faith works itself out in some manner, however, beginning with a cleansed, changed heart. I have two very close friends who believe that a person can lose his/her salvation. Imagine walking on eggshells every minute of every day, wondering if you have salvation or not.
James 2:24 You see that a person is justified by what he does and not by faith alone.
Which means the motivation for good works is focused on yourself ... to make sure you get there. Assurance of salvation allows the good works to be done in gratitude for what Christ HAS DONE for us ... not what we HOPE he will do if we have enough of them.