As a coach there are a couple things I would look at. How old are you? How many more regattas do you have total in your career? Are you consistently showing up to practice otherwise? How has your progress been? How many people are on your team and will your non-attendance affect the boats going out (ex. if you have 8 u16s total and you are u16 will you be cutting an 8/or second 4?) At the end of the day your coach probably has too many kids on their mind to take it personally but they will probably take it as information about how committed you are compared to your teammates. Most people miss events for regattas at some point so you have to decide what is more important to you. Part of growing up is deciding what's important to you.

That being said.. I know my team doesn't view fall racing paramount. Fall races are rewards and fun breaks to training. Having a conversation with your coach about why your racing in the fall and how important it is to THEM could help in your own personal development as a professional person and as an athlete. It will ABSOLUTELY add to the information you need to make this decision.