Good points all QuickSilver, but if it's any consolation, you know that the same thing will happen to them. My grandkids are lovable, cuddly, affectionate, etc., but you and I both know (and I refrain from popping my daughters bubble with this info when she's going on and on about them), that as they grow up, it will change and become something different. Good case scenario, they will still love their mom, but they're unlikely to give their lives for her. Bad case scenario, they will simply become distant and unreachable.
While I went through that process of trying to redefine myself once they moved out and I was no longer 'mommy' as I'd been for 20 years, I don't think I've ever felt disappointed as a result of the kinds of changes you mention because I had zero expectations on how it would turn out. If you don't 'expect' you can't be disappointed right? Then all the good things (if any) that come along in any relationship (children, friends, spouses, etc) are a blessing and a bonus. It's when we live with expectations of certain outcomes that we set ourselves up for disappointment. In my opinion anyway.