Oh, *that* south. I see. :-)
The chance of losing your STank to such a result is pretty slim though. It's about 1/18 at full wounds, 1/9 at 8-9 wounds, and still only 1/6 at 6-7 wounds. Result number 7 can be dangerous when you're down to 3 wounds or so but won't kill it otherwise, and it looks to me as if it still gets to take its armour save against #7 wounds (explicitly forbidden when suffering wounds from a cannon misfire, not mentioned here).
Did you notice that according to the wording of the rules you need to have a character - any character - in a detachment to benefit from HtL? Your Captain with HtL is in the parent. The parent can now roll break tests on 3d6 etc. A detachment benefits from the rule that "If a character with this rule is in a unit...". It doesn't need a Captain or GotE but a WH or wizard will do since all the accompanying characters benefit from HtL as part of the detachment...
I wouldn't be in the least surprised to find this FAQ'ed.