Well, yes, you still can farm him but it'll be a waste of keys; the win rate won't worth it. From experience I'd say it win only 30-40%
To put in picture. For 10 duels (cost 560 keys):
with ad hoc deck you get abt 34 drops at 40% win
with reliable farm deck you get abt 58 drops at 80% win
That's 22 more drops. And 40% is generous
I say use ad hoc when he's out. Lose nothing there. Spend keys? Nah