I had my DC very young (18 when I had DD) so we had never been without children until the last one went off to university. We'd always had an active social life, and were both working full time, so, in a way life was much easier! Yes, I missed them too, but we and they were happy and busy, and holidays were hectic and great fun - I never knew how many would be living with us / passing through. You, and they, move through these phases side by side, not co joined.
We loved watching them flourish, take off round the world, settle down, produce wonderful (of course!)l DGC and are now seeing the first DGD, 18, off doing Voluntary Community Service in her gap year. She has the best relationship ever with DD, but both knew it was time to go.