Hi Dan
I am a llama keeper rather than an alpaca keeper, but the same principles apply.
I wouldn't shear them with horse clippers, and in answer to your question I think they would be fine left until next year. As llama fibre does not have the same value as alpaca fibre we tend to shear less frequently, and as they get older the growth rate slows down. My llamas have not been shorn completely for several years, and definitely have only been done twice in the last eleven years. However as the fibre does not have a value I tend to hand trim them each year for their benefit with craft scissors, and let the fibre fall to the floor. They don't look as good but as you can see from the photos they look OK and it does not cause as much stress. I do this on my own in a small pen, but the animal is not restrained in any other way. If you want to use the fleece you would better to wait until next year when the professional can do it.