In II Kings 5, we learn about Naaman being saved from leprosy, and also that he does finally acknowledge the one true God (vs.15). But do we ever really know his relationship with God, as far as his soul and the way he worshipped God from then on?
Not much is said about Naaman after his return to Syria, which isn't surprising since the Old Testament focuses on Israel. We do know his intentions, "Yet in this thing may the LORD pardon your servant: when my master goes into the temple of Rimmon to worship there, and he leans on my hand, and I bow down in the temple of Rimmon-when I bow down in the temple of Rimmon, may the LORD please pardon your servant in this thing" (II Kings 5:18). So we know Naaman denounced the false gods of Syria.
The only other mention of Naaman was when Jesus used him as an example of how God at times gave blessings to Gentiles while ignoring the Israelites (Luke 4:27).