Modified participation is better than opting out completely.
If being in the midst of the celebratory chaos is too much for a child who is overwhelmed by sensory overload because of Sensory Processing challenges or autism, participating from a distance may allow him/her to be part of the celebration and remaining comfortable. If family and friends are gathered around the tree in the living room, hang out with your child in an adjacent room that the two of you selected in advance, and make it clear that it's socially acceptable. This way he/she can participate to the extent that feels manageable and you can spend time with friends and family.
Coming early to scope out the venue, and leaving on a high nite, before your child has a chance to decompensate will give him or her the confidence to attend another event.