If it vanished instantly then yes, but a huge number of packages on Central are mirrors from jcenter. There are not only theoretical competitors to Maven Central but an actual widely used one (jcenter/bintray), which is easier to use anyway. There's also jitpack too. So people could migrate pretty quickly to alternatives.
You're not technically wrong, but I bet that 90% of the projects or at least the examples have some sort of intentional or unintentional reliance on Maven Central, that would break the build if it weren't there. Even a lot of companies that set up internal repositories don't realize that they hit still are gonna hit Maven Central initially, before everything is bootstrapped, depending on how things are configured. It would reflect just really poorly on the Maven ecosystem (or any ecosystem alike, I have to assume, but know less about) if the canonical repository would just... "poof".
