I only buy a campaign when its Return to is available as it is the only way to properly store cards.

therefore my question : does anyone know when the circle undone and the dream eaters campaigns’ Return tos will be available ?

Can't give a date, but in the past, one "Return To..." release (what I think you are referring to) is put out between every new cycle. So the next Return will arrive after the Innsmouth cycle is complete, and the one following that after whatever the next cycle is.

1 hour ago, Eeyogre said:

Can't give a date, but in the past, one "Return To..." release (what I think you are referring to) is put out between every new cycle. So the next Return will arrive after the Innsmouth cycle is complete, and the one following that after whatever the next cycle is.

That's been the trend. The Circle Undone should get its "Return to..." box after Innsmouth finishes. The month before or after that we should receive War of the Outer Gods (if not sooner), the stand-alone that would have been at this year's GenCon & Arkham Nights.