I occasionally see news stories of a robbery or burglary where the perpetrator cops some scratch tickets along with the other stuff.
with the lottery folks simply be able to void that batch of tickets? or, even more, use those tickets to catch him if he tries to cash in?
As somebody who works with lottery daily, yes. As soon as it is reported as stolen (all vendors [really should] keep strict inventories on their lottery and basically treat it as they would cash), all stolen tickets will be invalidated and they will notnbe redeamable.
if somebody rips off a partial roll, can you tell exactly where the bad tickets begin?
Yes. They all have serial numbers, likely sequential so if a roll has serials 0005 through 00150 and some are stolen it should be very easy to tell. If the inventory records show 5 sales and only 00142 through 00150 are remaining, all cards from 00011 to 00141 can be safely assumed stolen and invalidated.