Yom Tov Sheni shel Galuyot

Question

1 = If one grew up in Israel and came to the U.S. to study -- and intends fully to return once their studies are complete ( e.g., after acquiring a B.A. ) -- I believe the law is to observe both days of yom tov. Correct ? 2 = Assuming that is correct, but instead chooses to "keep one day" ( which really is code for "I violate one day of yom tov" ), is this person considered observant ? 3 = For example, do they assur non-mevushal wine ? Can one eat at this person's house ? Are there any halachic problems that arise in connection with this scenario ? Thank you.