Let's just double-check. Am I right in thinking that you recorded on all 8 tracks, flipped the tape over, and when you played it back, track 5 was playing back (in reverse) something that had just been recorded by track 4?
If so, that means that the head and the connection to it is fine.
Remember that the R8 is a 2-head deck. One of those two heads is an eraser, which means that the audio head is doing double-duty for both recording and playing back. Hence if that track on the head can either record OR play back, it means the head is perfectly fine (in which case that the problem most likely lies in the channel card somewhere).
To answer your question about the head going open-circuit, that's the worst-case scenario. An 8-track record head like this consists of 8 coils, one for each track. If something utterly catastrophic happens, it is possible for the coil to melt on one or more tracks, which destroys the head element for that track. Ultimately an electrical circuit is a closed loop which electricity flows through. If a component fails such that electricity can no longer flow across it, it is said to be open-circuit because it's no longer a closed loop.