Traditionally final SR grades are done prior to graduation and the school sends them off very quickly. Colleges and SA's notify the counselors regarding when the transcript must be submitted by, thus, the GC's will have them there by that time. I highly doubt that it will not arrive until a month in as a plebe. Actually, at our DD's school they not only receive their diploma that day, but also their report card.
Think about it you don't take tests that final week, instead you are doing all of those fun things, like picnics and practices. The teachers are submitting your grades while you are doing those fun things.
Yes, they can rescind. ALL SA's have that option and state the appointment is conditional, and one of the conditions is grades. Failing a course can jeopardize your appointment. Believe it or not I know of one case this yr that a student with a principal nom had their appointment to the AFA rescinded due to grades. He was a ROTC college student and failed 1 course.
Failing and a D are 2 different things. Was this a class that would be considered by the USNA as a requirement? For example, USNA requires 4 yrs of Math, but maybe the HS only requires 3 to graduate. You can graduate, but now you don't have the required 4 yrs of Math for the USNA which will jeopardize your appointment.
Good luck. My suggestion would be to contact your BGO and discuss how or if this will impact your appointment.
It is rare that they rescind appointments. Are you positive you are going to fail? At this point you still have about 2 weeks to pull up those grades. Go to the teacher, explain your predicament and see if they will give you extra credit so you can pull it up to a passing grade.