I almost always have to redo ops because our group gets wiped and everyone leaves. I need to know how I can continue an op where I left off after the group is disbanded.

your only option is to go to fleet and try form the group saying that you are staring from a later boss

 

if it is a group finder ops then you could try jump into the group finder again.

have you enough knowledge of the content to explain tactics to first timers?

do you check if people have experience, with that level of content?

if HM, do you check others' gear?

why you generally wipe at the bosses? low dps, failing key mechanics...