Just be aware that fenders on a winter bike tend to accumulate snow in the winter. The tire kicks up snow, it gets kicked up into the fender, then it builds up enough to hit the tire so the tire is rubbing against it. This puts some stress on the fender as the tire scrapes against the snow and moving the snow back off the fender.
If you fender ever comes off and gets jammed between the tire and the fork on the front wheel, you will suddenly and immediately completely lose control of the bike without any chance whatsoever to react. If it happens on the back tire it's bad but usually you have a chance to react and keep the bike under control as it comes to lurching stop.
For this reason, I would not rely on zipties to hold on a fender, especially the front fender. When people lose control of the front tire that's when people break a collarbone or get thrown off their bike, there's no skill that lets you recover from completely losing control of the front tire (the back one is different).
Obviously it's your call, and on a mountain bike like that you do have more clearance than normal between the tire and the front fork, so things may not be as likely to jam up as with a more roady bike. But I wouldn't take the risk, I'd rather ride without fenders than have them held on with zip ties (particularly for winter riding).