Of course he can remove the bull if he wants to. If he wants to send a particularly strong message, he can auction it and stipulation of the sale that the bull may not be positioned anywhere in New York City, and make the subsequent story his art.

A corporate advertising campaign co-opts social media and a vacuous fawning politician into demanding its advert must stay and be worshipped, and the symbol of America's indomitable spirit and dynamism is packed into a shipping container and sent to Shanghai...

I think it'd be hard to say Di Modica had been "defeated" as an artist if that all unfolded... and he'd probably have quite a few million from the sale to take solace in (plus being able to charge the city copyright royalties when it commissions a replica replacement).