Soft Power reset by microcontroller
You could trigger a chip such as an LMC555 with the microcontroller input and use that to time the power-off.  Capacitively couple the microcontroller GPIO to the /Trigger input. 



The output can directly control the gate of a p-channel MOSFET (with 100R in series is good). Be careful this band-aid does not cause more problems than it solves- in particular make sure the control input and power is well bypassed to prevent it from triggering from EMI. 

If the latch-up is in the I2C devices you could safely interrupt power to them directly with the micro, leaving power on to the micro.