Hello BillKirst. Yes, you will.
That is one of the motivations for keeping declined meetings on the calendar. Even if you can't make it to the meeting synchronously (at the time others are meeting), you can still interact asynchronously (before and after the meeting) with them. This means not only accessing the chat, but also having access to attachments, recordings, transcripts or any other meeting collateral that might be of your interest.
By the way, there is yet another feature coming soon that will help you with staying up to date with meetings that you are not be able to attend: Follow. Follow lets the organizer know you can't attend but are interested in the meeting. And Follow will be available for all users, independently of Copilot purchase. 🙂 For more information on Follow, check out this video The new Microsoft Outlook for Windows & Copilot help you achieve more from 8:13 to 9:36.