How would an ASIC miner fail if the cooling does not work?
Ignoring risks from cables and connectors overheating, which seems to be the main fire risk.
So assuming an ASIC hash board has access to plenty of 12v DC power and the cables are over-engineered and all software safety mechanisms fail:
How hot will it get before it stops drawing power?
Or will it melt itself and cause a short circuit?
Let me tell You my expirience I had 4 years ago when I started my journy with company:
FlameIT - Immersion Cooling. Movie on main page is S9 the story is about

I have manage to buy Antminer S9 at super low price. I have paid less then PSU was worth alone (really nice Dell 2kW server PSU). That was gold hit

Anyway S9 was already not profitable at that time.
The story is. I have built my first immmersion coolling tank, put S9 inside and started my experiments. Everything was working fine, I was nicely heating water (summer) for my house + I had to open one radiator in basement to dissipate extra heat. Then I have closed that radiator and left house for a weekend forgetting to open it again

After I was back, my water was 75 oC hot and temperature measured on board was 90. Thankfully, S9 shutted down itself after going above 90oC. Thanks to immersion nothing wrong happend AT ALL to the device or house

The tank and water were just a bit hot

How other miners look in our best available synthetic fluid? Check that:
https://www.youtube.com/watch?v=sBgkyj-ILFkCheers! Paweł 'felixd' Wojciechowski, FlameIT