If I were to apply under UPenn’s ED program (being the only ED/EA school I apply to) and get in, am I obligated to go no matter what?
I assume you are thinking of applying ED to Penn next year because its ED application period is over for this year. The contract you sign (and this applies to all ED colleges) states that you agree to attend the college if admitted and agree to withdraw any other admission applications you have elsewhere. So in good faith you are obligated to go. If you have an intent to not attend if admitted, then don’t apply ED.
Nevertheless, a percentage admitted ED do not end up going and the usual reason is the parents. The finical aid package offered turns out to be too low for the parents to be able to afford sending you to Penn. If the parents decide not to accept the financial aid package and cannot negotiate a better one, Penn and any other colleges with ED will let you avoid the agreement to attend.