Final answer:
The correct form to use in the sentence is 'he,' as it functions as a subject pronoun. 'Him' is incorrect because it is an object pronoun and the person in question is performing the action of deciding, not receiving it.
Step-by-step explanation:
The correct answer is 'he'. This sentence requires a subject pronoun, not an object pronoun. 'He' is the subject form, and 'him' is the object form. So, the correct sentence is 'At the last minute, he and his friends decided to take a trip to Las Vegas.'
In English, the choice of pronoun depends on its role in the sentence. When the pronoun is doing the action, as in this case, the subject form is required. Using 'he' indicates that the person along with his friends made the decision and is the subject of the action.
It is also important to note that the trend towards using 'they/them/their' as non-gendered pronouns does not apply here, since the person's gender appears to be known and the pronoun is singular, referring specifically to 'he' or 'him' alongside 'his friends'.