I would always go into a cycle planning on loosing about 25-30 % of the gains post cycle depending on what gear you use of course. If you gained 30, then I am guessing you used some gear that put water on you and you will loose that weight.
If you go into a cycle planning that, then you should not be too disappointed afterward.
I take precautions to keep water off, so I don't fluctuate much after a cycle. My last cycle of Prop/Tren/Winny, I did not loose 1lb of my gains post - but that is becuase of the gear I used.