Missing the first leg of my booking

Hey guys, quick question. It's become a possibility that I may have to miss the first leg of a journey I have coming up, I was wondering if I do this will I still be able to use the return leg?
I seem to remember this being asked before, somebody said when they did this, the return journey just disappeared and they weren't able to log into their booking, I just want to clarify this, thanks.
I seem to remember this being asked before, somebody said when they did this, the return journey just disappeared and they weren't able to log into their booking, I just want to clarify this, thanks.