I'm sorry he missed it last year and was hurt, unfortunately those things happen.
There are so many ways you can get hurt in day to day life but thankfully don't. Missing out on rollerskating with friends due to a fear of injury for a child's performance is a bit overkill. Realistically, you could trip down the stairs, fall in the shower/bath, get in a car accident, stub your toe so hard you break it, and so forth, yet I am sure you don't restrict these things.
When my boys learned to skate this summer they crashed many times but they were fine, just bruised.