Yeah, something like this Virgin can expensively source third party connectivity to keep their business SLAs intact. If they did that for consumer broadband they'd have to bump their prices to a level people would then complain at.
While accidentally cutting a gas line suggests process opportunities, it does feel entirely reasonable that they stopped work on the cable until that was sorted.
Nobody wants outages but the answer is clear: If you really must have always-on broadband, don't go with just one supplier, and do pay the extra to get the SLAs. Don't want that expense? Accept that sometimes things will go down.
(My second supplier is my mobile service provider; lower bandwidth than Virgin but I've yet to lose both at once, and still have power to the house)