Can good cardiac collateral flow keep you alive and healthy?

In short : Yes...But this partially offset by the burden of CAD already present that led to collateral a in the first place...There is still a high risk burden.

Somewhat: Extensive collaterals can be very protective. It is even possible to have a heart attack with no symptoms, and no perceivable damage if the collaterals are developed enough at the time of a vessel occlusion. On the other hand, having occluded vessels secondary to cholesterol plaque isn't exactly "healthy", even though you are feeling well.