I think more likely we could be in an anti incumbency era where incumbent presidents fail to win reelection. Keep in mind this was also the case from 1836-1896 when no incumbent outside Lincoln and Grant got reelected so its not like its unprecedent.
If Trump wins he obviously won’t be able to run again so that would mean we would go at least 12 years without a two term president since we would not have had a president with two consecutive terms.
Oh sure but his VP almost certainly would be the nominee (given how weak the gop bench is) and they probably would lose .
Keep in mind in that time period no incumbent VP was elected president either