It should save the simulation when you do 'save' or 'save as'. I never had problems on p6 but on p7 it frequently forgets all about the simulation as soon as I save and sometimes when I do a render.
It may be a Mac specific bug.
I now use 'spawn morph' as facehugger does. It has an advantage of being able to continue to the simulation from the end of the previous one if you wish too.
Another strategy is to write the cloth out as a '.obj' file and read it back in.

"I paint that which comes from the imagination or from dreams, or from an unconscious drive. I photograph the things that I do not wish to paint, the things which already have an existence."
Man Ray, modernist painter
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