Send a notification when someone changes username or deletes their account
...so everyone in their network or follows know. Just something nice so people just don't randomly vanish with us knowing it.
Changing names, Sure. But deactivating account, highly disagree. This suggestion would negate any privacy a person wishes to retain would also be considered Stalking.
Personally, there are people that follow me, that I do not follow and do not wish to have them see me at all. Blocking only goes so far, especially for unpaid members.
Same goes for changing screen names.