O2 sensor fell off Triangle of death and other lights on dash now

The first thing to do is read the trouble codes.

It sounds like your car has a couple of unrelated problems.

 

I want the rest of the "sensor fell off" story!

That is a heated oxygen sensor, so the four wires include a power supply to the sensor's heater. If those wires get torn apart when the sensor falls off, and the heater power happens to touch something grounded, it can sometime blow a fuse, sometimes damage a power transistor inside the ECM, sometimes both, resulting in trouble codes and strange behavior.

I think most reports of this have been from owners whose entire catalytic converters have, ahem, fallen off. Is there any chance someone was trying to liberate your catalytic converter, maybe got interrupted?

 

have to agree with the above. Likely a short circuit due to those shredded wires popped a fuse or damaged something.

If I remember right, it gets power from the 15A EFI fuse in the underhood fuse box. Provides power to engine control and hybrid control systems. I'm not sure how the car would have continued to run if that fuse popped, but maybe it popped the fuse after you got home and started working on it. Would be great if that's your problem.
Pull the cover off and it should be the 15A fuse at the top right corner.
There should be a spare 15A fuse near the top center of the fuse box

 

That power to the heater is controlled by a power transistor inside the ECM. There used to be a list of "Murphy's Law Corollaries" that got passed around in techie shops, and one of them was "a transistor that is protected by a fast-blowing fuse will protect the fuse by blowing first".

Doesn't always happen, but if it does, I think there's a trouble code for it. If the transistor is kaput, the ECM is needed.

Found this in a gen 3 repair manual, but haven't checked if it's the same in gen 2:

 

The ecm also receives power from the EFI fuse. Good luck, hope you get it sorted out.

And because I'm bored while waiting for our guests to arrive this evening:

In simple terms.
EFI fuse outlet splits to two wires.

One goes to the ECM pin 6 labelled BATT

The second supplies the EFI M relay, whose output wire then splits to 5 wires at Junction Connector J1.
1. supplies cannister purge module pin 9 (vent valve) and fuel vapor containment valve
2. ECM at pin 4 labelled +B
3. MAF meter pin 1 +B, the purge valve, and the air/fuel ratio sensor B1S1 +B
4. Oxygen sensor B1S2 +B
5. the fuel pump via relay