Was doing some Lst 4 weeks( 4 weeks) last night and snapped about 12 cm off the main. Plant didn't really notice. Not so much as a wilted leaf. Good growth this morning.
Was all panicky when it happened. First grow, think its grooving as well.
I've never purposely topped an Auto, but I'm sure that breakages happen in nature, so it will carry on, only downside is you lost a cola. You could try potting up the snapped limb, you never know.