My friend has an '01 Mustang and she blew out a spark plug.

She put an insert in and the insert sticks to the plug rather than staying in the head.

Started it up and it seems to run fine.

Question is, should she just call it done and fixed or is this a time bomb?

Thanks as always!

She'll ultimately need a new head. The aluminum will be further damaged every time the insert comes out.

I'd suggest looking into installing a 'Keensert'. The installation includes a way of locking it in so that it will not come out.
KS

Thanks!