Star Wars: Dark Forces/WMG

Jaden got a power boost from being blasted with the staff.
Explains how he/she became capable of carving through the Disciples of Ragnoss like a lightsaber through butter.

Rosh died stupidly not long after the light side ending of Jedi Academy.
… or else, like Kyle and Jaden (along with Keyan Farlander from X-Wing and Maarek Steele from TIE Fighter), he would have been mentioned somewhere in the subsequent novels…