I think you are correct, and the trucks would not roll.
My impression is that if riots broke out and were larger than say 3 city blocks (pick a number, this is a guess on my part), that law enforcement would switch from being in an active intercession mode to being in a lock down and contain mode, being ready to go in and do cleanup when/if things settle down.
Of course resources would be dedicated to protecting valuable infrastructure things like hospitals, power units, etc.
History says the police will go to protect city hall, the mayors house, etc. IOW, it will go to protect the physical safety of TPTB, even if the critical infrastructure burns to the ground. (Seriously, watch that Rodney King documentary video I just reposted.)