I regularly visit Adam West's feed. I knew Adam and going to see some of his corny posts (like Moose Wayne) are an occasional comfort and not only remind me of him but remind me of watching the tv series as a child with my late father.
Sadly, I've noticed that DMs don't seem to be forever on twitter as all of our private messages to each other are all gone, the bulk were gone before he even passed away.
Given his account is verified I would hope that Twitter keeps that content as long as the service survives, but for those with family and friends that have passed that weren't high profile, they may also take comfort in going through then posts of those accounts and this is kinda blah.
I get it from a cost view, it costs money to keep all of that data but I somewhat feel that a company that has user created content is socially obligated to maintain that content as long as they continue to have that product or until the user wants it removed whichever comes first.