What happened to Yisro after he went back to Midyan to convert his family? שמות 18:27 Also, is he mentioned anywhere after in tanach? (him, not his descendants)
He obviously returned to the Midbar later on because he is mentioned again in BaMidbar (Numbers) 10:29
וַיֹּ֣אמֶר משֶׁ֗ה לְ֠חֹבָ֠ב בֶּן־רְעוּאֵ֣ל הַמִּדְיָנִי֘ חֹתֵ֣ן משֶׁה֒ נֹֽסְעִ֣ים אֲנַ֗חְנוּ אֶל־הַמָּקוֹם֙ אֲשֶׁ֣ר אָמַ֣ר 'ה
Moses said to Chovov the son of Reuel the Midianite, Moses's father-in-law, We are traveling to the place about which Hashem said
The Pesukim continue with Yisro saying that he want to return to Midyan. Moshe asks him to remain with them in them in the Midbar . The Ramban(ibid) based on the Yerushalmai in Bikkurim says that he stayed with them and went with them to Eretz Yisroel.
In Shoftim 1:16 there is a reference to his descendants living with the Jews in Eretz Yisroel
There are a few different opinions. In the pesukim, it says ויחד which Rashi interprets as he left to Midyan, converted them to Judaism, and I guess lived out the rest of his days there. Next, there’s actually an argument over what happened first; Matan Torah or the story of Yisro. I won’t outline all the arguments, but basically according to Ramban I believe, Yisro came after Milchemet Amalek to Bnei Yisroel and then went with them to Har Sinai to experience Matan Torah with them and help them understand the Torah.