ah so you mean cut the wire and use the relay plug as a bridge so to speak, do you know what pins it needs to be attached to? i'm assumiong pins 1 and 3 according to the manual
PIN 1: NORMALLY CONNECTED
PIN 2: NORMALLY OPEN (SHOULD BE GROUND THEN)
PIN 3: NORMALLY CONNECTOR
In reality would the 10 seconds it takes to shut off without a pump during boot or during use really cause a massive overheat?
In Aquaero 6 correct pins are are 1 and 3.
In older Aquaero 5 pin 3 is still common contact, but normally closed is pin 2.
https://aquacomputer.de/tl_files/aquacomputer/downloads/manuals/aquaero_5_6_en.pdf
Those are always connected together when relay is in inactive/"relaxed" state, allowing motherboard to pull PS ON to ground.
When relay is powered, normally closed contact opens cutting PS ON signal.
https://electronics.stackexchange.com/questions/30952/can-you-clarify-what-an-1no1nc-switch-is
Normally open pin is left unconnected.
Unless relay is connected in parallel with power switch of the case to use motherboard's own logic.
In that case it's normally closed pin which isn't connected to anything. (like in that graph with Aquaero 5)
But functionality of power button in running PC can be affected by power settings of Windows.
From shutting down PC to initiating sleep mode, or even doing nothing.
There might be settings for that also in BIOS.
So there's the caveat of it possibly doing nothing with certain Windows settings.
In which case it would be up to CPU's thermal throttling/thermal shutdown to do the job.
Though if you have also GPU in the loop, CPU's protections won't help that.