In Parshas Yisro (Shemos 18:25) Moshe appoints the Chiefs of the 10, 50, 100 and 1,000.
"וַיִּבְחַר מֹשֶׁה אַנְשֵׁי־חַיִל מִכָּל־יִשְׂרָאֵל וַיִּתֵּן אֹתָם רָאשִׁים עַל־הָעָם שָׂרֵי אֲלָפִים שָׂרֵי מֵאוֹת שָׂרֵי חֲמִשִּׁים וְשָׂרֵי עֲשָׂרֹת׃"
Moses chose capable men out of all Israel, and appointed them heads over the people—chiefs of thousands, hundreds, fifties, and tens;
"וָאֶקַּח אֶת־רָאשֵׁי שִׁבְטֵיכֶם אֲנָשִׁים חֲכָמִים וִידֻעִים וָאֶתֵּן אֹתָם רָאשִׁים עֲלֵיכֶם שָׂרֵי אֲלָפִים וְשָׂרֵי מֵאוֹת וְשָׂרֵי חֲמִשִּׁים וְשָׂרֵי עֲשָׂרֹת וְשֹׁטְרִים לְשִׁבְטֵיכֶם׃ "
So I took your tribal leaders, wise and experienced men, and appointed them heads over you: Chiefs of thousands, chiefs of hundreds, chiefs of fifties, and chiefs of tens, and officials for your tribes.
But we never hear about them actually doing anything else. Notably, in Beha'alothcho (Bemidbar 11:16) Moshe appoints a set of 70 Elders to help deal with the people. There is no indication that there was an overlap between the Chiefs and the 70 Elders.
How long did the Chiefs retain their positions? What do we know about them except for the fact that they were appointed?
A quick search of Tanach does not seem to find them later on in history.