What is the correct way of using Anko Coroutines extensions?

So I am migrating an example app from RxJava to Kotlin/Anko Corountines and I am wondering if I am doing the best (first) approach of it:

fun getPopulationList() {
    val ref = asReference()

    async(UI) {
        try {
            ref().setCurrentState(ViewState.State.LOADING)
            val background = bg {
                repository.populationResponse().execute().body()
            }

            ref().let {
                it.response = background.await()
                it.mvpView?.onGetData(it.response)
                it.setCurrentState(ViewState.State.FINISH)
            }
        } catch (e: Exception) {
            e.printStackTrace()
            ref().mvpView?.onError(e)
        }
    }
}

I am using an MVP architecture where my Presenter base class had a CompositeSubscription and in the onDestroy's fragment or activity method simple unsubscribe and clear the CompositeSubscription object. But i am wondering if the asReference() function from Anko Coroutines does the same and there is no need to save a list of Deferred<T> and then iterate it and cancel one by one.

BTW if I add a Thread.sleep(5000) to simulate a big transaction and destroy the Fragment I can see in the logcat the HTTP response even after the fragment is not visible/destroyed while with RxJava doesn't happen, so I think I am not using properly.

UPDATE

 fun getPopulationList() {
    val ref = asReference()

    job = launch(UI) {

        try {
            ref().setCurrentState(ViewState.LOADING)
            val background = bg {
                Thread.sleep(5000) //simulate heavy IO

                if (isActive) {
                    repository.populationResponse().execute().body()
                } else {
                    return@bg null
                }
            }

            ref().let {
                it.response = background.await()
                it.mvpView?.onGetData(it.response)
                it.setCurrentState(ViewState.FINISH)
            }
        } catch (e: Exception) {
            RestHttpExceptionHandler().handle(UI, e, ref())
        }
    }
}

I am able to cancel the coroutine while calling job.cancel() in onDestroy() method but to make it work I have to check if the job is active or not and that translate into an if/else and a return or not data. Is there any better way to return something when the job was cancelled?