Hard to say, since I'm not a doctor and am not familiar with that particular procedure. If I were in your shoes, 3 days after it, do an average ride, see how it feels. When it comes to the day of the ride, if you decide to go forward, the situation is this: it's a charity ride. You'll have regular rest stops. There'll be a SAG wagon in all probability. They usually hand out maps/cue sheets with a number to call for SAG assistance. Check the route map. Many charity rides have shorter distance options. If they all start out over the same route, and have different return points, you can always bail out on a shorter route. And if things go really bad, call the SAG number or wait for the van along the road. SAG vehicles generally sweep the course at regular intervals. But if you experience pain or discomfort on the pre-event rides, don't go. You're not going to lose very much fitness, if any, with 3 days off the bike.