[ptero]

In principle, yes, IPC can fail between different versions of the same software. However, the chances that communication will fail between new version and some other utility are IMO much higher. A surprise comm failure between two copies of the same software (even different revisions) usually makes developers look pretty bad.

Some versions are known to be incompatible and most Linux distributions do a very good job of recommending and doing a restart of affected services in a way transparent to users. I have been running Linux and home and at work for years, almost never restart those workstations and, as far as I can tell, never had problems from piecemeal upgrades. My 2c.