It's both a blessing and a curse, as anybody who's accidentally emailed the wrong people or hit send before finishing editing knows, but it's the most powerful thing about email (and SMS or even fax for that matter!) - you get your own copy.
When companies have kindly sent me their entire customer list (by using CC in place of BCC) I see there are very few domains in it outside of the major free email providers, and those that remain are mostly for their work or small business. A personal or family domain is very rare.
You can renew a domain for ten years in advance and easily transfer between registrars (and email providers, I use Fastmail), so it's a lot more reliable for the (very) long term than a third-party service.
I have no huge issue with moving to a more IM-based interaction as my default, but I've yet to find one that is actually compatible with them all. I need 3-5 apps to communicate to everyone right now, and in a few years some of those will be gone and new ones will be added.