I am a skier not a snowboarder, so that over let's get back to basics. ACL injuries are far more common amongst skiers than snowboarders, but no-one stops skiing unless they want to! Return to any sport after an ACL injury is partly mind over matter, but more importantly a really good rehab programme and high level of fitness.
It depends entirely on you if you go back or not. Many of the snowboarding fraternity have had knee injuries of one type or another, the professionals rehab well and go back. For you, it depends on what your level is and more importantly why your graft failed.
If your graft failed because you did not rehab properly, then my gut feeling is that if you follow the same route again, perhaps snowboarding is not for you. Proper rehab, good strength training and fitness are essential for all sports.
If the failure had nothing to do with snowboarding, then by all means go back, but make sure you are fully fit, that your equipment is well maintained and that you do not go back "hell for leather" on the first day. It may well be a good idea to stay out of the Park and half pipes initially as well.

But once you are back to full strength and no longer "think" about your knee, why not.

I have been told by many professionals that if I were a snowboarder, I would have far fewer worries than I do as a skier. Knees are not under the same stress with snowboarding
once you are a proficient rider. Unfortunately for me my first injury occurred 3 days before I was due to start learning to snowboard, so my chances of achieving that now are well and truly history. But I still ski, most weekends in the snow season plus most of my annual leave allowance, and on glaciers out of the main ski seasons. I have moderated my skiing due to the accumulated abuse and consequently poor state of my knees, but I'm still there.
I had a total revision carried out in August 2008 and along with it a whole lot of other stuff done in there, I thought my skiing days were over. My surgeon told me otherwise and had me back on my skis (albeit gingerly) 5.5 months later. I skied about 10 days that season. In December 2009 I took part in an intensive performance training course as preparation for returning to instructing. I passed, but have since chosen not to instruct any more other than on as a just for fun basis for friends.
My point here is YES YOU CAN! You have to want to do something badly enough to do the work and to be able to moderate your sport to accommodate your weaknesses post injury. You have to be physically fit and also mentally fit.
I watched Benni Raich race to 12th place in a World Cup Giant Slalom last weekend he snapped his ACL last March at the World Championships in Garmisch-Partenkirchen. So a mere 7 months later, there he is racing down an ice wall (the race was on a glacier) at speeds of about 60mph without a brace! Proper strength training and focussed post operative rehab, will help you get to do what you want.
See you on the slopes in Austria some day maybe!
Sue
