Consider the following two sentences:
What's the difference between these two sentences? How does the bolded part affect the meaning?
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In this context, 帰る can mean either "to come home" or "to go home". Essentially, it means "to return home", which can imply either direction (coming or going). So, we use the ～てくる construction (movement toward the speaker) to make it clear that the person is coming home.
We can also use the ～ていく construction (movement away from the speaker), but I think it's far less common with 帰る.
= X will come home.
= X will go home.
= X will return home.
So, if you were out and about, you could say something like,
= I'll go home at 6.
Or, someone might say to you,
= Are you going home at 6?
But, if you were already at home,
= I came home at 6.
I tried to explain this as best as I could, and how I generally think of this construction.
行く is used when you say someone is 'going somewhere' and 来る is used when you say someone is 'coming'. The verb you use is dependent on YOUR POSITION.
If I was in America right now and I wanted to say "my friend is going to go to Japan", I would translate it as 友達は日本に行きます。This is because she is "going away" relative to my position.
On the other hand, if I were in Japan and my friend, who lives in America, was coming to Japan, I would translate it as 友達は日本に来ます。He is "coming to me".
You can think of 〜ていく and 〜てくる in the same way.
Let's assume A-さん is the subject of your sentence.
A-さんはうちへ帰ります。 A-san will return home. (Awkward translation but necessary to highlight the difference)
A-さんはうちへ帰ってきます。 A-san is going to come home.
Using the logic explained with 行く and 来る, you are already at the destination (that is, A-san's home) and A-san is returning home, which is also towards you.
Using 〜ていく with this sentence, 「A-さんはうちへ帰っていきます」, you are assuming the position of someone not at A-san's destination, so when A-san is 'returning home', he is not 'coming to you'. He is 'going away from you' and so the sentence would be interpreted as "A-san is going to go home".