events.py

# models.py
from .tasks import send_event


class Event(models.Model):
    is_async = models.BooleanField(default=False)

    # ...
    def _send(self):
        # do sending stuff

    def send(self):
        if self.is_async:
            return send_event.delay(self.pk)
        return self._send()


# tasks.py
from django.apps import apps


def send_event(pk):
    event_model = apps.get_model("events.Event")
    try:
        event = event_model.objects.get(pk=pk)
        event._send()
    except event_model.DoesNotExist:
        pass

events2.py

# models.py
class Event(models.Model):
    is_async = models.BooleanField(default=False)

    # ...
    def _send(self):
        # do sending stuff

    def send(self):
        if self.is_async:
            from .tasks import send_event
            return send_event.delay(self.pk)
        return self._send()


# tasks.py
from .models import Event


def send_event(pk):
    try:
        event = Event.objects.get(pk=pk)
        event._send()
    except event_model.DoesNotExist:
        pass