If you cancel your exchange and don't book another week on the same phone call, II will give you a replacement week. That replacement week will be valid for an exchange within one year of the date you cancel. The replacement week won't necessarily have the same trading power as your original week.
If you cancel less than 60 days but at least 14 days prior to your scheduled check-in, you will not be permitted to request a replacement exchange until you are within 59 days of when you want to travel. If you cancel between seven and 13 days of your scheduled check-in date, you will not be permitted to request a replacement exchange until you are within 30 days of when you want to travel. If you cancel less than seven days prior to check-in, you are out of luck.
Also, you should generally cancel as soon as you realize you can't use the exchange. Your trading power for the replacement week, even outside of the 59-day window, may be reduced, depending on how far in advance of the scheduled check-in date that you cancel. The only offsetting factor would be if you know you won't be able to use the replacement week within a year. That might dictate delaying your cancellation action, even though your trading power will likely be reduced.
You'll pay another exchange fee when you redeem the replacement week for a confirmed exchange.