I firmly expect Trump to challenge the results of this election and even refuse to leave the WH. I wrote about it here: https://medium.com/illumination-curated/100-days-until-inauguration-day-df01351add0b
However I see no scenario where Trump wins Election Day voting in a landslide. There are enough battleground states that count absentee ballots in advance of the election to give a clear picture on election night.