I've hit a case yesterday jailbreaking an iPad 2 where I was stuck on the the part where the device will reboot several times at the end of the jailbreak and a second case where it was at the beginning of the process where a reboot was required at one point. In the first case, I got caught with the 1st reboot. It hung there for about 10 minutes trying to reboot. I did a hard reset, and it just kept continuing and the device was fine afterwards, the jailbreak was successful. Then the second time, I was stuck in the middle of a reboot process during the initial reboot that's needed. I did a hard reset, and the progress bar proceeded.
But, if Evasi0n comes up with an error of some sort, rejailbreak the device from the beginning. It's always better to be safe by rejailbreaking the device rather than causing harm to it.