That may happen--only time will tell, but since the Democrat team brought up the Biden's in their attempt to prove their case, and the Biden's are certainly part of the case against Trump, then
if witnesses are called (Bolton and others) for the Democrats, then rest assured that the Bidens will also be called to testify in the Ukraine corruption senario.
It is just a shame that this impeachment process since the House first commenced the process is along party lines and has since the start been and continues to be Democrats against Republicans, rather than
what the founders of the Constitution envisioned as a bi-partisan coherent impeachment process in the House and likewise bi-partisan trial in the Senate.