Advice please - Heater Matrix failure

[BensZ4MC]

My car has been with Mercedes approved bodyshop due to some damage to the plastic under tray and side skirt - when this accident happened the heater seem to stop blowing hot.

The Bodyshop have said the Heater Matrix is leaking and this has nothing to do with the accident so the insurer wont pay for a replacement. The SLK is 2012, 38k miles, FMSH - is the heater matrix likely to fail on its own?

Thanks