The only real time that LLYs die is during the LOCKER patch.... If its a stock full flash or a full flash that isn't locking the ECM to the V2/V3, I've stopped many of full flashes mid flash without bricking. The only time the bootloader gets touched is when the Seed Key is changed during the lockpatch.... only during that specific time is it important to not lose power.....

If you're doing a read like you say and it locks up, figure out what is talking on the bus and shut it up or bench flash. But in a read scenario is perfectly safe to pull the ECM fuse or batteries to reset the ECM to get it talking again.