(...including 8.8.4.4)
Obviously a lot of DNS resolution attempts in the internet would fail, but beyond that I see so many scripts and uplink tracking logics purely based on the fact, that 8.8.8.8 / 8.8.4.4 are ICMP / UDP 53 reachable. What would happen?
There are plenty of good alternatives out there. I tend to not use Google's DNS but I do run into it. I'd' have to do an audit and switch over the stragglers.
How would it affect you if 8.8.8.8 service was terminated immediately?
I would not know. My firewall caches the root zone, talks directly to the tld servers and caches their responses.