Helicoil failure

I have a 98 sunfire that suddenly blew out a spark plug last week. The mechanic put in a helicoil and told me that while he could not guarantee it he figured it would last at least 25k miles.

The coil held, but the spark plug they put in failed after only about 100 miles. And of course, when I tried to remove it (very gently) the coil came right out.

At this point, I just want to get the car home without having it towed (50+ miles.) so i'm trying to find out if I have any options.

For instance, can I try again with a larger helicoil? Or is there an alternative solution?

Rather confused as to how the spark plug just blew out of the head. In plain blunt english, if the plug came out of your head it needs to be repaired correctly....as in a new head.

If the Heli-Coil just unscrewed I would have another one installed with careful attention payed to properly securing the insert from screwing out in the future. Anyone trained in installing thread inserts will know how to do this.