So I was trying out greenskins with wurzag and stumbling along. I finally reached Waagh at the same turn that I also managed to lose all my armies. So I thought "let's waagh anyway and I'll just spawn some new lords and have them fight and get joined by bonus units to fill out the ranks". I didn't realise you only get as many bonus units as you had original ones at the time you unleash it. So I unleashed it, built two lords and each one jumped at an army of enemies only to look behind them and go "hey, guys? Hello?".
I guess I should have checked the wiki first. https://totalwarwarhammer.gamepedia.com/Call_to_WAAAGH
Mind you I still don't know how long they would have stuck around if I had managed to use them to wipe out the target capital. Can you just give yourself a new target right away and keep rolling or does your balance go to zero once you have won?
And I know you might get some number of your leader's special units but what proportion of those and what number of other units turn up? If I had 20 units and was fighting in the badlands would I eventually grow to N special units and 20-N savage orcs?