When running this test case:
==========
$ cat TestExit.java
public class TestExit {
  public static void main(String... args) {
    System.exit(-1);
  }
}
==========

with fastdebug or slowdebug (turns on VerifyBeforeExit), we don't actually execute the code path that perform the verification.

The VM exits inside the this->loop() call:
==========
  // Wait for VM_Operations until termination
  this->loop();

  // Note the intention to exit before safepointing.
  // 6295565 This has the effect of waiting for any large tty
  // outputs to finish.
  if (xtty != NULL) {
    ttyLocker ttyl;
    xtty->begin_elem("destroy_vm");
    xtty->stamp();
    xtty->end_elem();
    assert(should_terminate(), "termination flag must be set");
  }

  // 4526887 let VM thread exit at Safepoint
  _cur_vm_operation = &halt_op;
  SafepointSynchronize::begin();

  if (VerifyBeforeExit) {
    HandleMark hm(VMThread::vm_thread());
    // Among other things, this ensures that Eden top is correct.
    Universe::heap()->prepare_for_verify();
    // Silent verification so as not to pollute normal output,
    // unless we really asked for it.
    Universe::verify();
  }
==========

this->loop() terminates when we execute:

#0 vm_exit (code=-1) at src/hotspot/share/runtime/java.cpp:532
#1 0x00007ffff69b3dc0 in JVM_Halt (code=-1) at src/hotspot/share/prims/jvm.cpp:478
#2 0x00007ffff5ac6bcd in Java_java_lang_Shutdown_halt0 (env=0x7ffff001eb80, ignored=0x7ffff5bed610, code=-1) at src/java.base/share/native/libjava/Shutdown.c:41

and vm_exit schedules a VM_Exit vm operation, that runs inside this->loop().

VM_Exit::doit calls vm_direct_exit:
==========
void vm_direct_exit(int code) {
  notify_vm_shutdown();
  os::wait_for_keypress_at_exit();
  os::exit(code);
}
==========